Activation of which of the following genes leads to entrance into the lysogenic cycle?

• A. N, cro, and O genes
• B. O, P, and Q genes
• C. Int and xis genes
• D. cIII genes

Answer: (C)

Verified step by step guidance

1. Understand the lysogenic cycle: The lysogenic cycle is a viral replication cycle where the virus integrates its DNA into the host cell's genome, allowing it to be replicated along with the host's DNA without causing immediate harm to the host.
2. Identify the role of Int and xis genes: The Int (integrase) gene is responsible for integrating the viral DNA into the host genome, while the xis (excisionase) gene helps in excising the viral DNA from the host genome when the virus decides to enter the lytic cycle.
3. Compare gene functions: The N, cro, and O genes are involved in the lytic cycle, promoting viral replication and cell lysis. The O, P, and Q genes are also associated with the lytic cycle, facilitating replication and assembly of new viral particles.
4. Focus on cIII gene: The cIII gene is involved in the regulation of the lysogenic cycle by stabilizing the cII protein, which promotes the expression of the Int gene, thus favoring lysogeny.
5. Conclude the activation process: Activation of the Int and xis genes is crucial for the virus to enter the lysogenic cycle, as Int integrates the viral DNA into the host genome, establishing lysogeny.