A lambda bacteriophage integrated into the genome of E. coli became lysogenic. Upon UV irradiation, it is expected that the lytic cycle will be induced. Due to mutations that have occurred as a result of UV irradiation, you find that the lambda bacteriophage remains in the lysogenic state and lysis is impaired.
Mutations in the following genes have been proposed to explain this observation:
A. cI gene, protease cleavage site
B. cI gene, DNA binding site
C. recA gene of E. coli
D. ruvA gene of E. coli
Which one of the following options represents all correct statements?

Correct option is C

Correct Answer:
(c) A and C
Explanation:
UV irradiation activates the SOS response in E. coli, leading to RecA-mediated autocleavage of the CI repressor, which is essential for induction of the lytic cycle.
A mutation in the protease cleavage site of CI (A) would prevent CI inactivation, maintaining lysogeny.
Similarly, mutation in the host RecA protein (C) would block CI cleavage altogether, again preventing entry into the lytic cycle.
Information Booster :
· Lambda phage switches from lysogeny to lysis via CI repressor cleavage.
· RecA acts as a coprotease during the SOS response.
· Loss of CI cleavage locks the phage in lysogeny.
· UV induction relies on host–phage regulatory coupling.
Additional Information (Incorrect Options):
B (cI DNA-binding site): Loss of DNA binding would derepress lytic genes, favoring lysis, not lysogeny.
D (ruvA): Involved in Holliday junction resolution, not directly required for SOS-mediated CI cleavage.
Hence, options containing B or D are incorrect.