Genetic Switch in Lambda Phage | Video Lecture by Priya Khadgawat #geneticswitch #bacetriophages

Summary

This video explores the genetic switch mechanism in lambda bacteriophages, viruses that infect bacteria. It explains how these phages can toggle between a dormant (lysogenic) state and an active (lytic) state, regulated by complex gene expression patterns. The script details the lambda phage structure, key genes involved in this process, and the roles of proteins like the lambda repressor, Cro, and C2 in regulating the transition between states. Environmental factors such as UV light can induce the switch to the lytic cycle, leading to the production of new phage particles. The video delves into the intricate molecular control that governs these processes.

Takeaways

• 😀 Lambda phage is a bacteriophage, which is a virus that infects bacteria and can alternate between two states: dormant (lysogenic) and active (lytic).
• 😀 In the lysogenic state, lambda phage integrates into the host chromosome and does not harm the bacterium, whereas in the lytic state, it replicates and destroys the bacteria.
• 😀 Lambda phage genome consists of a single DNA molecule wrapped in a protein coat, which is injected into the bacterial cell, triggering either the lysogenic or lytic cycle.
• 😀 The transition between the lysogenic and lytic cycles is controlled by the regulation of specific genes, including the lambda repressor and Cro protein.
• 😀 Lambda repressor protein binds to the operator sites in the phage genome, inhibiting the expression of other genes, maintaining the lysogenic state.
• 😀 Under UV radiation, the lambda repressor is inactivated, allowing Cro protein to promote the lytic cycle by binding to the operator sites with opposite effects.
• 😀 The two main regulatory proteins in the lambda phage are the lambda repressor (Cl) and Cro, which are transcribed in opposite directions and have key roles in the switching mechanism.
• 😀 Positive regulation of gene expression involves the lambda repressor activating its own gene expression, while negative regulation occurs when it inhibits Cro synthesis by binding to specific operator sites.
• 😀 Inducing factors such as UV light lead to a decrease in repressor concentration, which triggers the shift to the lytic cycle, allowing phage production and bacterial cell lysis.
• 😀 The C2 protein plays a crucial role in promoting the lysogenic cycle by stabilizing the lambda repressor protein, while environmental factors like nutrient availability can affect the stability of these proteins and the cycle choice.

Q & A

What is the genetic switch mechanism in lambda bacteriophages?

The genetic switch mechanism in lambda bacteriophages refers to the process by which the virus alternates between two states: the lysogenic cycle, where it integrates into the host genome without killing the host, and the lytic cycle, where it replicates and causes the host cell to burst, releasing new virus particles.

What is the role of the lambda repressor protein in the lysogenic cycle?

The lambda repressor protein controls the lysogenic cycle by binding to operator regions on the phage DNA, turning off all other genes except its own, and preventing the transition to the lytic cycle. It acts as both a positive and negative regulator of gene expression.

How does the lambda phage switch from the lysogenic to the lytic cycle?

The switch from the lysogenic to the lytic cycle is induced by environmental factors like UV light, which causes the lambda repressor to be cleaved. This inactivation of the repressor protein leads to the activation of the Cro protein and the initiation of the lytic cycle.

What is the function of the Cro protein in the lytic cycle?

The Cro protein promotes the lytic cycle by binding to operator regions on the phage DNA and inhibiting the transcription of the lambda repressor. This leads to the production of proteins required for the phage to enter the lytic cycle and replicate.

What are the key promoters and operators involved in the genetic switch of lambda phage?

The key promoters involved in the genetic switch are prm (repressor maintenance) and pr (right promoter). The key operator regions are r1, r2, and r3, which regulate the expression of genes involved in the transition between the lysogenic and lytic cycles.

How does UV light induce the switch to the lytic cycle?

UV light activates a protease that cleaves the lambda repressor, leading to the loss of its ability to bind to the operator sites. This cleaving activates the Cro protein, which promotes the switch to the lytic cycle.

What is the role of the C2 protein in regulating the lambda phage cycle?

The C2 protein helps establish the lysogenic cycle by activating the repressor (lambda repressor) and aiding in the integration of the phage DNA into the host chromosome. It also regulates the expression of other proteins involved in the cycle.

What environmental factors influence the stability of the C2 protein and the choice between the lysogenic and lytic cycles?

The stability of the C2 protein is influenced by environmental factors such as the nutrient conditions of the host bacteria. In rich media, active proteases degrade C2 protein, promoting the lytic cycle, while in poor media, the absence of active proteases allows the accumulation of C2 protein, favoring the lysogenic cycle.

What is the function of the N protein in the lambda phage lifecycle?

The N protein acts during the early phase of infection by preventing transcription termination at specific sites (nut sites). This allows the continued transcription of genes necessary for the establishment of the lytic cycle.

How do N and Q proteins regulate the transcription process during the lytic cycle?

The N and Q proteins prevent the premature termination of RNA transcripts. N protein acts early in the infection by binding to nut sequences, while Q protein acts later in the lytic cycle to extend the transcription of head and tail genes, essential for phage replication and assembly.