The genetic switch controlling whether a bacterium enters the lytic or lysogenic cycle relies on the binding of which two proteins?

Cro and lambda

Explanation:

In the lysogenic cycle, the viral DNA is within the host DNA, while in the lytic cycle the viral DNA is separated from the bacterial cell, replicating independently from the bacterial DNA. The cro and lambda are DNA-binding repressor proteins of the bacteriophage lambda which bind to different operator sites, i.e., different genetic sequences found between the promoter and the structural gene. These proteins are known to have complementary functions in lytic and lysogenic cycles. The cro protein repressor binds non-co-operatively to operator DNA regions, while the lambda protein contains a domain (carboxy-terminal) that binds co-operatively to operator regions.