What is a Type I Restriction Enzyme?

Summary

Type I restriction enzymes are complex proteins made up of a specificity protein, two methyltransferase proteins, and two restriction endonuclease proteins. These systems recognize a specific bipartite sequence on DNA but do not have a predictable cleavage pattern. After binding to DNA, they translocate using ATP and create a double-stranded break upon encountering a second complex. This process requires ATP, S-adenosyl methionine, and magnesium ions. Currently, no type I restriction enzymes are commercially available. For more information, visit NEBrestrictionenzymes.com or REBASE.neb.com.

Takeaways

• 😀 Type I restriction enzymes consist of three proteins functioning as a single protein complex.
• 😀 The protein complex includes a specificity protein, two methyltransferase proteins, and two restriction endonuclease proteins.
• 😀 Type I restriction systems recognize a bipartite sequence with half sites separated by 5-8 non-specific nucleotides.
• 😀 These enzymes do not produce a predictable cleavage pattern.
• 😀 The protein complex acts as a molecular motor, using ATP to translocate along the DNA until encountering a second complex.
• 😀 When two protein complexes meet, they create a double-stranded break in the DNA.
• 😀 Cleavage occurs after translocation, meaning the cleavage site is not fixed.
• 😀 Type I restriction enzymes require ATP, S-adenosyl methionine, and magnesium ions to function.
• 😀 There are currently no commercially available type I restriction enzymes.
• 😀 For more information on restriction endonucleases, visit www.NEBrestrictionenzymes.com or REBASE at REBASE.neb.com.

Q & A

What proteins make up Type I restriction enzymes?

Type I restriction enzymes are composed of three proteins: a specificity protein, two methyltransferase proteins, and two restriction endonuclease proteins.

How do Type I restriction enzymes recognize DNA sequences?

Type I restriction enzymes recognize a specific bipartite sequence, where the half sites are separated by 5-8 non-specific nucleotides.

What is unique about the cleavage pattern of Type I restriction enzymes?

Type I restriction enzymes do not produce a predictable cleavage pattern. This is due to their cleavage occurring after translocation along the DNA molecule.

How do Type I restriction enzymes cleave DNA?

Once the protein complex binds to the DNA, it translocates along the DNA using ATP until it encounters another complex. This results in a double-stranded break.

What factors are required for the function of Type I restriction systems?

In addition to ATP for translocation, Type I restriction systems require S-adenosylmethionine (SAM) and magnesium ions for their activity.

What is the role of ATP in the function of Type I restriction enzymes?

ATP is used as an energy source for translocating the restriction enzyme complex along the DNA molecule until it encounters a second complex, leading to cleavage.

Why is the cleavage site of Type I restriction enzymes not fixed?

The cleavage site is not fixed because cleavage occurs after translocation, meaning that the enzyme moves along the DNA before cutting, resulting in a variable cleavage location.

Are Type I restriction enzymes commercially available?

Currently, there are no Type I restriction enzymes available for commercial use.

What additional resources can provide more information about restriction endonucleases?

For more information about restriction endonucleases, you can visit www.NEBrestrictionenzymes.com or REBASE, the restriction enzyme database at REBASE.neb.com.

What makes Type I restriction enzymes different from other types of restriction enzymes?

Type I restriction enzymes differ from others because they do not produce a predictable cleavage pattern and require ATP, S-adenosylmethionine, and magnesium ions for their activity. They also translocate along the DNA before cutting it, which is not typical for other restriction enzymes.