How would mutations that inactivate each of the following genes affect the determination of the lytic or lysogenic life cycle in mutated λ phage strains? Explain your answers. cII and cro

Key Concepts

Lytic and Lysogenic Cycles

The lytic and lysogenic cycles are two distinct pathways that bacteriophages, like λ phage, can follow after infecting a bacterial host. In the lytic cycle, the phage replicates rapidly, leading to the destruction of the host cell and the release of new phage particles. In contrast, the lysogenic cycle involves the integration of the phage DNA into the host genome, allowing it to replicate along with the host cell without causing immediate harm.

cII Protein

The cII protein is a key regulatory protein in λ phage that promotes the lysogenic cycle. It stabilizes the expression of genes necessary for lysogeny, including the integration of phage DNA into the host genome. If mutations inactivate the cII gene, the phage is less likely to enter the lysogenic cycle, favoring the lytic cycle instead, which can lead to increased phage production and host cell lysis.

cro Protein

The cro protein is another regulatory protein in λ phage that antagonizes the action of cII and promotes the lytic cycle. It represses the expression of genes required for lysogeny, thus favoring the production of new phage particles. Mutations that inactivate the cro gene would lead to reduced lytic activity and potentially allow for lysogenic development, as the balance between cII and cro is crucial for determining the phage's life cycle.