RNA Transcription 3b'
Summary
TLDRThis lecture delves into the intricacies of transcription and RNA processing, focusing on the initiation phase and the pivotal role of sigma factors in recognizing promoter sequences. It discusses the transition from initiation to elongation, akin to DNA replication, where RNA polymerase reads the template strand and synthesizes RNA. The session also covers the mechanisms of transcription termination in prokaryotes, contrasting intrinsic and rRNA-dependent termination. The lecture further explores the complexities of eukaryotic transcription, highlighting the involvement of multiple RNA polymerases, general transcription factors, and the role of enhancers and silencers in regulating the process.
Takeaways
- π¬ The lecture discusses the process of transcription and RNA processing, focusing on the initiation, elongation, and termination of transcription in both prokaryotes and eukaryotes.
- π The importance of the sigma factor in prokaryotes is highlighted, as it recognizes promoter sequences and initiates transcription.
- 𧬠Elongation in transcription is compared to DNA replication, with RNA polymerase moving along the template strand and synthesizing RNA in a 5' to 3' direction.
- π Termination of transcription in prokaryotes can occur through two mechanisms: intrinsic (row-independent) and extrinsic (row-dependent), involving specific sequences and proteins.
- 𧲠Intrinsic termination involves a hairpin loop and a string of A's on the template strand, which causes RNA polymerase to pause and release the RNA.
- π Extrinsic termination in prokaryotes relies on the rho protein, which binds to the RNA at a specific site and disrupts the DNA-RNA hybrid to terminate transcription.
- π Eukaryotic transcription is more complex, involving a larger genome, the presence of a nucleus, and the need for RNA processing and export to the cytoplasm.
- 𧬠Eukaryotes have three different RNA polymerases, each with distinct promoter sequences and functions, including the transcription of ribosomal genes, small RNA genes, and protein-coding genes.
- π Transcription factors play a crucial role in eukaryotic transcription, binding to promoter elements and facilitating the binding of RNA polymerase to initiate transcription.
- π The process of transcription initiation in eukaryotes involves a specific order of transcription factor binding, leading to the formation of a pre-initiation complex and the start of transcription.
Q & A
What is the role of the sigma factor in the initiation of transcription?
-The sigma factor is crucial for the initiation of transcription as it helps the RNA polymerase recognize and bind to the promoter sequences, specifically the -10 (Pribnow box) and -35 regions, enabling the start of RNA synthesis.
How does the elongation process of transcription differ between DNA replication and RNA synthesis?
-Although elongation in transcription is similar to DNA replication, the key difference is that RNA polymerase moves along the DNA template strand from 3' to 5', synthesizing RNA in the 5' to 3' direction using ribonucleotide triphosphates instead of deoxyribonucleotides.
What is the function of the 'transcription bubble' mentioned in the script?
-The 'transcription bubble' is a region of local denaturation that forms behind the RNA polymerase as it moves along the DNA template. It consists of the single-stranded DNA and the newly synthesized RNA, and it allows for the continuous synthesis of RNA while the DNA re-anneals behind the bubble.
What are the two mechanisms of transcription termination in prokaryotes?
-The two mechanisms of transcription termination in prokaryotes are Rho-independent termination and Rho-dependent termination. Rho-independent termination involves the formation of a hairpin loop and a string of U's in the RNA, causing the RNA polymerase to pause and release the RNA. Rho-dependent termination requires the Rho protein, which binds to a specific site on the RNA and moves along it until it reaches the RNA polymerase, causing termination.
What is the significance of the poly U stretch in RNA during Rho-independent termination?
-The poly U stretch in RNA, resulting from a string of A's on the template strand, plays a role in Rho-independent termination by creating weak A-U base pairing that facilitates the release of the RNA from the DNA template, thus ending transcription.
How does the Rho protein contribute to Rho-dependent termination of transcription?
-The Rho protein contributes to Rho-dependent termination by binding to the RNA at the Rho Utilization Site (RUT site), using ATP to move along the RNA, and catching up with the RNA polymerase. It then sterically hinders or unwinds the DNA-RNA hybrid, causing the release of the RNA transcript and termination of transcription.
What are the differences between prokaryotic and eukaryotic transcription in terms of complexity?
-Eukaryotic transcription is more complex than prokaryotic transcription due to the presence of a larger genome with more genes and non-coding DNA, the necessity of RNA export from the nucleus to the cytoplasm, and the presence of chromatin. Additionally, eukaryotes have three different RNA polymerases, each with their own set of genes to transcribe, and require processing of precursor mRNA, including the removal of introns and addition of exons.
What is the role of the TATA box in eukaryotic transcription?
-The TATA box, also known as the Hogness box, is a DNA sequence element found in the promoter region of many eukaryotic genes. It plays a crucial role in the initiation of transcription by providing a binding site for the TATA-binding protein (TBP) and other transcription factors, which help assemble the transcription pre-initiation complex.
How do enhancers and silencers regulate transcription in eukaryotes?
-Enhancers and silencers are regulatory DNA sequences that can be located at a distance from the promoter and can influence the rate of transcription. Enhancers bind activator proteins that stimulate transcription, while silencers bind repressors that inhibit transcription. They can modulate the transcription machinery's assembly and function, either promoting or suppressing gene expression.
What is the significance of the order in which transcription factors bind during eukaryotic transcription initiation?
-The order in which transcription factors bind is significant as it ensures the proper assembly of the transcription pre-initiation complex. For example, transcription Factor 2D (containing TBP and TAFs) binds the TATA box first, followed by the binding of other factors like 2B, RNA polymerase II, and then 2F and 2H, which together form the complete initiation complex and trigger the start of transcription.
Outlines
π¬ Transcription and RNA Processing
This paragraph discusses the process of transcription initiation, emphasizing the role of the sigma factor in recognizing promoter sequences (Theus 10 and Theus 35) and binding to the core RNA polymerase. It explains how the sigma factor can be released once transcription starts, transitioning into the elongation phase. Elongation is compared to DNA replication, with RNA polymerase moving along the template strand, synthesizing RNA using ribonucleotide triphosphates. The paragraph also describes the formation of a transcription bubble, where the newly synthesized RNA and the DNA separate as transcription proceeds. Finally, it introduces the concepts of intrinsic and Rho-dependent termination mechanisms in prokaryotic transcription, detailing how RNA polymerase recognizes termination sequences to end transcription.
𧬠Intrinsic and Rho-Dependent Transcription Termination
This section delves into the specifics of intrinsic (Rho-independent) and Rho-dependent termination in prokaryotes. Intrinsic termination involves the formation of a hairpin loop and a string of Us in the RNA, which cause the RNA polymerase to pause and eventually release the RNA, terminating transcription. Rho-dependent termination, on the other hand, requires the Rho protein binding to a specific site in the RNA, which then moves along the RNA and interacts with the RNA polymerase to terminate transcription. The paragraph illustrates these mechanisms with figures and explains how mutations in the sequences involved can affect the termination process.
π Complexity in Eukaryotic Transcription
The paragraph contrasts eukaryotic and prokaryotic transcription, highlighting the increased complexity in eukaryotes due to a larger genome, the presence of a nucleus, and the need for RNA processing and export. It mentions that eukaryotes have three different RNA polymerases, each responsible for transcribing specific types of genes. The paragraph also discusses the structure of eukaryotic promoters, which can vary and may include elements like the TATA box, CAT box, and GC-rich regions. These elements are recognized by general transcription factors that facilitate the binding of RNA polymerase and the initiation of transcription.
π§ Eukaryotic Transcription Initiation and Regulatory Elements
This part focuses on the initiation of transcription in eukaryotes, detailing the order in which transcription factors bind to the promoter region. It describes the role of the TATA box and other promoter elements in facilitating the binding of RNA polymerase and the assembly of the transcription machinery. The paragraph also introduces the concept of enhancers and silencers, which are regulatory sequences that can modulate the transcription process by binding activator or repressor proteins, respectively. The discussion includes the role of the carboxy-terminal domain of RNA polymerase in the initiation of transcription and how phosphorylation of this domain can trigger the start of transcription.
π Elongation and Regulation of Transcription
The final paragraph discusses the elongation phase of transcription in eukaryotes, which is similar to prokaryotes, with RNA polymerase reading the template strand and synthesizing RNA. It also touches upon the role of enhancers and activator proteins in regulating transcription, providing an example of the yeast UAS (Upstream Activator Sequence) as a strong enhancer. The paragraph briefly mentions that the next lecture will cover termination of transcription, suggesting a continuation of the discussion on the regulation of gene expression.
Mindmap
Keywords
π‘Transcription
π‘Sigma Factor
π‘Elongation
π‘Termination
π‘Promoter
π‘RNA Polymerase
π‘Eukaryotic Transcription
π‘Introns and Exons
π‘General Transcription Factors
π‘Enhancers and Silencers
Highlights
Initiation of transcription is crucial, and the sigma factor plays a key role in recognizing promoter sequences.
The core RNA polymerase and sigma factor bind to the promoter region, initiating transcription at specific sites.
Elongation of RNA is similar to DNA replication, with RNA polymerase moving along the template strand and adding complementary nucleotides.
Termination of transcription in prokaryotes can occur through intrinsic or Rho-dependent mechanisms, involving specific sequence recognition.
Intrinsic termination involves a hairpin loop and a string of Us in the RNA, causing the RNA polymerase to pause and release the RNA.
Rho-dependent termination requires the Rho protein, which binds to the RNA and moves along it, eventually disrupting the DNA-RNA hybrid.
Eukaryotic transcription is more complex due to a larger genome, the presence of a nucleus, and the need for RNA processing and export.
Eukaryotes have three different RNA polymerases, each responsible for transcribing different sets of genes.
Promoters in eukaryotes have multiple recognition sites, including the TATA box, CAT box, and GC-rich boxes, which interact with general transcription factors.
The order of transcription factor binding in eukaryotes is crucial for the initiation of transcription.
Transcription Factor 2D, containing the TATA binding protein, is the first to bind, initiating the formation of the pre-initiation complex.
The carboxy-terminal domain of RNA polymerase 2 is phosphorylated, triggering the start of transcription.
Enhancers and silencers are regulatory sequences that can modulate transcription by binding activator or repressor proteins.
The yeast UAS is an example of a strong enhancer that can significantly increase transcription when present.
Elongation in eukaryotes follows a similar process to prokaryotes, with RNA polymerase synthesizing RNA along the DNA template.
Transcripts
all right this is the second part of the
transcription and RNA processing
recorded lectures so we were talking
about initiation of transcription
importance of the sigma factor and being
able to
recognize the promoter sequences Theus
10 and Theus
35 so here we have the core RNA plase
Sigma factor in there and recognizing
the promoter region here Theus 35 Theus
10 to get to the RNA plas where we can
start transcribing
RNA I talked about how when um that
starts the sigma Factor can be released
because its job is done we then move on
to elongation and elongation is very
similar
to DNA replication we can look just take
quick look at this slide here so you
have the template Strand and again three
prime here five Prime here so RNA
polymerase is moving
down a template strand it's reading it
so to speak in a 32 five Prime Direction
okay going down this way and then it's
bringing in nucleotides that are
complimentary to the template Strand
and again it uses ribonucleotide
triphosphates it'll cleave off two those
phosphate groups pyrro phosphate so that
you can form the energy to form that
that calent Bond
there so this just shows again you got
the coating strand or the non-template
Strand has the uh same sequence as RNA
made u c a u or t c a and going along
the template strand there so RNA plary
slides along the
DNA goes to the template strand making
complimentary RNA um slides along 3 to
five Prime Direction so it can
synthesize the RNA in 5 to3 Prime pyrro
phosphate is lease we just looked at
that in the last slide and same um base
pairing rules except that you have U
instead of T um so again um elongation
occurs very much like DNA
replication it moves along um the DNA
strand three prime to five prime it
moves about in procaryotes about 30 to
50 nucleotides per second um you give
you an idea DNA plase moves about 2,000
nucleotides per second so DNA
replication much faster than
transcription as the pmer moves along it
creates what I've mentioned before a
transcription bubble um behind the
bubble the DNA DNA reenal and displaces
the newly synthesized RNA so as the DNA
starts to reenal here the RNA the red
Parts displaced outside of the
bubble all right so let's get
to then termination of
transcription so how does RNA plase know
when it's reached the end of a gene when
to stop transcription well it knows when
it reaches a termination
sequence and there are two mechanisms by
which this can occur in procaryotes
there is the intrinsic or row
independent
termination and there is then the second
way the row dependent
termination so we'll talk first about
the intrinsic or row independent
termination so the Terminator sequence
in R independent termination consists of
a string of A's on the template strand
resulting in a string of U's or a poly U
stretch in the RNA that is
made this um termination sequence also
consists of a sequence of two-fold
symmetry which allows a hair pin form
Upstream of the A's and use okay
Upstream again to the left or to the
five Prime end the sequence of twofold
symmetry is G and C rich and forms a
complimentary intramolecular hydrogen
bonds taking on the form of a hairpin
Loop that's followed then by this run of
use in the RNA now remember RNA pulas is
about 50 nucleotides long RNA plase will
move down the DNA this hair pin is
thought to slow down the plase somewhat
as it's going along and causing the
plase to pause and when the plase pauses
this weak a and u DNA RNA base pairing
releases the RNA thus ending
transcription so again words sounds kind
of funny let's take a look at how this
is happening here so here's the
DNA here's RNA plas moving down at some
point it transcribed over here this GC
rich sequence that had this um com that
can that had this two-fold symmetry in
it so it could form complimentary
intermolecular hydrogen bonds and so it
forms this hair pin Loop all right and
as RNA polymerase is going it makes
hairpin Loop RNA polymerase it's this
hairpin Loop sort of get stuck in the
RNA plates it slows down and then it
makes all these U's and A's or the A's
and the DNA U's and the RNA here and you
have this weak unaa binding and it falls
apart and so termination happens so
here's
another picture here sort of showing it
so here's these again row independent
termination G's and C's Rich um
complimentary sequences so as
transcription takes place transcribe
this region transcribe that region it
folds up as a hair pin Loop and again
RNA polymerase is huge it's way like
this here and this hair pin Loop gets
stuck in RNA plas and so it transcribes
this 's and a as it gets stuck it pauses
these dissociate transcription then is
terminated here's another figure here
showing this um hairpin Loop so here's
the twofold Symmetry here there's a
transcription they can form this hairpin
Loop because these G's and C's
complimentary base be and so the
question is how do scientists know this
really is necessary for termination well
they know because as you can see here
they made mutations in these G's and C's
region which didn't allow a hairpin Loop
to form and when they did that when they
mutated these so the herin loop conform
then termination didn't happen correctly
okay in the same way if they deleted a
bunch of the uh A's appear they used in
form and they also then didn't get
proper termination so they have a
hypothesis they look at the sequence and
say hey look what's happening maybe this
is responsible or you go and then you do
the experiment say yeah if we with this
it no longer works
right okay so that was an intrinsic or
row independent termination the second
kind of termination is row dependent
termination for genes that are
terminated by row dependent termination
they do not have that polya sequence so
they don't form a
polyu sequence in the RNA and they often
don't have a hair pin region sometimes
they do but often times they don't here
the row protein which is a hexamer so
it's six parts put together binds to the
RNA at the the rut site so the row
protein binds to the rut site the rut
site stands for row
utilization site okay R for row UT for
utilization site um so it's a site where
the row protein utilizes or binds to the
RNA so what ends up happening um is this
row or sorry this rut site is just
Upstream of the termination site while a
polymerase pauses again at the
termination site again if there's a
herin Loop or for some unknown other
reason the row protein binds to this rut
site and slides along the RNA it uses
ATP hydroly ATP for energy to slide
along the RNA it then catches up with
the RNA
plase and somehow sterically hinders it
to disrupt the DNA RNA hybrid which then
releases the transcript or stops
transcription so let's take a look at
what that looks like in some figures so
here's the DNA here there's the row
recognition site or utilization site
gets transcribed in the RNA PL keeps
going okay
somehow it pauses here this row protein
binds and it starts using ATP to move
along here it reaches and during the
pause it reaches the RNA here causing
that complex to separate I have another
figure showing very similar
thing is
transcribing here's the doesn't show the
rut site but the RO hexer binds here so
it goes pauses at the Terminator Okay
the p is pause Terminator the row
proteins moving up here unwinds that DNA
RNA hybrid somehow or sterically hinders
something which separates RNA from the
DNA then terminates okay so the exact
I'm not completely clear on the exact
mechanism um when I learned in grad
school was thought it was something sort
of steric hindrance that that row
protein had with the plase we've been
reading different places and in this
slide where it's um unwinding the DNA
RNA hybrid but it's doing something to
cause termination of transcription at
that point by separating the DNA from
the
RNA all right so let procaryotic
transcription again there's going to be
lots of similarities between procaryotes
and UK carots and let's cover some of
the differences here now uh eukariotic
transcription is more complicated than
procaryotic transcription just like UK
arotic replication was more complicated
than procaryotic replication UK carots
have a larger
genome consisting of more genes and more
non-coding DNA while eoli has 900 genes
per 1 million base pairs ukar only have
nine genes per million base pairs so a
lot of extra DNA UK carots also have a
nucleus all right therefore RNA must be
exported out into this cytoplasm somehow
so this isn't really transcription but
what happens after the RNA is
transcribed there's another set of
events that have to occur to get that
RNA out into the
cytoplasm in addition to the larger
genome genes have exons and introns that
must be processed in the nucleus before
RNA can be exported okay so another step
so it doesn't really influence the
transcription per se but there's a
processing step that has to occur to
remove parts of the RNA before the RNA
can be moved out into the cytoplasm UK
carots also have chromatin okay or they
have more protein wrapped around their
DNA so that DNA is wrapped around these
histone proteins and there's some
regulation of the transcriptional events
that is also that is actually due to
those proteins or the chromatin
structure so there just more
complexities into uh the control of
transcription then there are three
different RNA polymerases made up of
several polypeptides and they each
transcribe their own set of genes so
there's one RNA plase for procaryotes
there are three for ukar so RNA plase
one transcribes mainly ribosomal genes
or R RNA genes um we'll talk about R
rnas in ribosomes in a minute or in a
little bit here um but there's the 18s
5.8s and 28s ribosomal genes that are
transcribed by RNA plas 1 R plase 3
transcribes mainly small RNA genes um
they transcribe T rnas they transcribe
the 5sr RNA and they transcribe these SN
rnas are the small nuclear RN the plase
we're going to focus on um mainly is RNA
plase 2 okay middle one here because RNA
p 2 transcribes protein coding genes so
they transcribe
mrnas and a few uh small nuclear rnas as
well but primarily they are the the RNA
Pras 2 is the plase that transcribes
protein coding genes and will be the
main focus of what we talk about we'll
just give some mention RNA plase 1 and
three so each of these RNA plas is
recognized as their own promoter
sequence RNA plase 1's promoter is not
well characterized and it's uh but it is
Upstream of the start site while RNA
pmer 3 promoter is actually internal to
the gene so it's actually Downstream or
yes sorry it's Downstream of the start
site which is different than what we
were talking about RNA Pates to promot
will be upstream and what we'll talk
about here so just a couple of images
here um just threedimensional structures
of RNA plases you can see form this
clamp like structure the donut sort of
shape this opening here that surrounds
the DNA similar to DNA plases you see it
opening here and the DNA being red in
the the middle there so just a little
bit of idea of how it binds um couple of
differences then in uh procaryotic
versus eukariotic transcription it's RNA
plase makes RNA that RNA can then
immediately be used for translation in
bacterial cells there's no membrane
bound
nucleus and yeah whereas in UK carots
right you get this membrane bound
nucleus then you also have precursor
mRNA which we talk about you have
introns and exons so you got to get rid
of those introns we'll talk more about
this so there's these processing steps
and then you got to get that RNA out
into the cytoplasm where transcription
can then occur
all right so transcription of protein
coding genes or transcription by RNA
plase 2 so promoters for protein coding
genes are best characterized in UK carot
RNA plas 2 transcription plus one again
is the initiator region right the first
nucleotide put on and when transcription
starts the promoter region has several
different sites in it and all these
sites don't necessarily have to be there
some can be there some can't we'll talk
about the sort of the best or most
well-known sites um the first site on
the negative side there - 255 or about
-30 is the Tata box or hoges box it's
called the Tata box because that's the
consensus sequence ta ta pretty similar
to the prol box that has lots of T's and
A's in it slightly different location
hogness just the name of the individual
that um was responsible for discovering
that um sequence um further Upstream -
80 - 90 or a couple more what you call
proximal promoter elements proximal
means close to so close to the start
site the initiator region um and these
are called the cat box and the GC Rich
boxes um cat box just because that's a
consensus sequence there c a a and GC
Rich boxes are exactly that they have
lot of G's and C's um and that could be
variable you can have long regions
several GC boxes and again you might
have some or not yet
and um I forgot to point out this
initiated region is not only the
location where initiation occurs but
there's also uh sequences in there that
are thought to play a role in this start
of transcription so recognized um within
the
promoter um so there's again there's
this great variation in eukariotic
promoters um not all promoters have all
of these sequences so promoter sequences
in ukar are recognized by transcription
factors or what are called General
transcription factors to to facilitate
RNA plas to binding so where Sig where
the sigma factor helped RNA plas bind in
procaryotes in UK carots there's going
to be a multiple uh mult there going to
be multiple numbers of transcription
factors General transcription factors
and that are going to help RNA plas bind
to the promoter and start transcription
they are named um a through H so trans
they're labeled here transcription
Factor 2A means general transcription
factor that interacts with um RNA plase
two so transcription Factor two
interacts AR p 2 a you have
transcription Factor 2 b c d and so on
um so if they're transcription factors
that interacted with RNA plas 1 they'd
be transcription Factor 1 a and so on
and so forth so the the number here say
tells you which um RNA plase they uh
interact with so here we go um start
side transcription plus one so there's a
region here that helps within the
promoter minus 25 you got the Tata box
there further Upstream then GC boxes Cat
boxes can be present all of which are
helping with um The Binding of RNA plase
so that transcription can start um so
initiator region position Tata box C box
GC box relative positions where they can
be found um transcription factors that
bind to them we'll talk about uh Tata
binding protein here this um One that
binds to the initiated region in the
Tata box mainly there are also other
various transcription factors that are
involved in binding to these some of
these other
areas um this region here again
initiation so the plus one site and
again this shows 30 I said minus 25 30
somewhere around there you got the Tata
box and Upstream promoter elements more
of these elements you get the cat box
there's a GC Rich region GC Rich region
there's another cat box there um showing
these regions can
be um there in the promoter to help with
transcription
so in vetro experiments so in test tubes
have been done to try and figure out
what transcription factors bind where
and in what order in order for
transcription to start and I think I
have another slide here we'll get to
there we go to talk about this so UK
carotic initiation so how does the
initiation transcription take place in
UK carots the order of The Binding
then um discovered from inv vitro
transcription factors in vitro
transcription experiments where that D
needs to be involved first followed by a
which I haven't put here because a can
sometimes um be excluded
b r plas itself and
f e and H okay so there's an order to
these so d
first A and B rnaase 2 and F together
and E and then H okay so initiation of
RNA plas 2 transcription transcription
Factor
2D binds the hoges box or the Tata box
okay creating an initial committed
complex all right so the first event
that occurs transcription Factor
2D contains the Tata binding protein tbp
the Tata binding Protein Plus taffs TAF
which stand for Tata binding protein
Associated factors okay so trans Factor
2D is actually multiple proteins
together the Tata binding Protein Plus
taffs let's see if we
have something here this one doesn't
necessarily show it but it's showing the
first step transcription Factor 2D
binding there here you have trans
description Factor 2D is this big one
here and part of that is the Tata
binding protein actually all in blue
here is
um transcription Factor 2D in tata
binding protein is part of that uh
structure transcription Factor 2 B after
d binds tab box transcription Factor 2B
can
bind and recruits RNA plas to in trans
rtion factor to F forming What's called
the minimal
transcription um complex and again a is
involved um with B but it's it was found
to be dispensable in in vro
studies this complex this minimal
transcription
complex sorry um next after the minimal
transcription complex 2E and 2H combined
which complete the initiation complex
this initiation complex is sufficient
for low level of transcription or or
basil
transcription the start of transcription
is believed to be triggered by the
phosphorization of the carboxy terminal
domain of the RNA pmer beta subunit okay
RNA plas will sit down that uh region it
has at its carboxy end okay or carboxy
terminal domain it uh has a region that
needs to be phosphorated to sort of set
it in motion to make it go so let's take
a look at some figures if we can look
here so there's D binding and again B
comes in and a would be involved too
inside the cell which recruits F and the
plase here preinitiation or close
complex it's preinitiation complex there
then you get H and E sorry H and E then
gives the whole pre-initiation complex
and then it can start and so CDT of RNA
plas 2 it's our K boxal terminal domain
um you see the p4s here it gets
phosphorated and that's then what starts
the process this next one doesn't show
the start of the process but you got RNA
plase here D get all the other BF and
there's a in this particular picture and
this one showing um uh other proteins
involved so we'll talk about enhancers
and silencers later in the course but
they're talking about other proteins
that bind to other sequences in DNA that
can then help this process assemble more
quickly or or um start um faster so more
regulatory sequences that are helping
this event to
occur so then once it starts then we get
into the elongation stage and we'll come
back to this and jumping ahead um just a
little
bit all right so as I said there's these
other sequences that help regulate the
enhancers then the way they regulate
transcription they're located different
regions of the genome they can be
further Upstream than those promoter
elements they can be really far away
actually and they're specific in that
they bind activators which are proteins
then that help them bind the basil
transcriptional apparatus and they help
enhance transcription so their name is
aole right they are enhancers they
enhance transcription by binding
activator proteins silencers then can
help repress transcription or silence
transcription by binding repressors that
would then interact or not allow this um
Machinery to start transcribing uh one
of the very first enhancers was
discovered in yeast cells and it's
called the yeast uas or Upstream
activator sequence and it's a really
strong enhancer you put it in front of
most any Gene in an experimental setup
and it will really Drive um
transcription quite well all right so
let's get to we got to initiation C boox
terminal domain enhancers B activators
silencers by repressors so how does
elongation go well elongation occurs in
the same way in UK carots as it does in
Pro carots right that RNA pmer is going
to move along it's going to read the
template strand it's going to put in
these um nucleoside triphosphates cleave
off to the phosphates make those calent
bonds and
um all right so um we'll wrap up here
and then we'll start talking about
termination and the next
um lecture for this unit
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