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. N

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.

Gene Function in Phage Life Cycles

Specific genes in λ phage are crucial for determining whether the phage enters the lytic or lysogenic cycle. For instance, genes like cI and cro play pivotal roles in regulating the switch between these cycles. The cI gene promotes lysogeny by encoding a repressor protein that inhibits lytic gene expression, while the cro gene favors the lytic cycle by repressing lysogenic genes.

Mutations and Their Effects

Mutations that inactivate genes involved in the lytic or lysogenic cycles can significantly alter the behavior of λ phage. For example, a mutation in the cI gene may prevent the establishment of lysogeny, leading to a predominance of the lytic cycle, while a mutation in the cro gene could result in a failure to initiate the lytic cycle, favoring lysogeny instead. Understanding these mutations helps elucidate the genetic control of phage life cycles.