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. 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 cell. 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.

Role of the cro Gene

The cro gene in λ phage is crucial for regulating the switch between the lytic and lysogenic cycles. It encodes a protein that promotes the lytic cycle by inhibiting the expression of genes necessary for lysogeny, such as cI, which encodes the repressor protein that maintains the lysogenic state. Mutations that inactivate the cro gene can disrupt this balance, potentially favoring the lysogenic cycle.

Gene Regulation in Phage Life Cycles

Gene regulation is essential for determining the life cycle of λ phage, as it involves complex interactions between various regulatory proteins. The expression of genes like cro and cI is tightly controlled by environmental signals and the state of the host cell. Mutations that affect these regulatory genes can lead to altered responses to stress or changes in the host environment, influencing whether the phage enters the lytic or lysogenic cycle.