30. The following statements are made about the E.coli SOS response to DNA damage:
    A. RecA-DNA filament complex stimulates the autoproteolytic activity of the Lex A repressor.
    B. RecA is activated due to the blunt ends of double strand breaks caused damage inducing agents.
    C. The SOS response includes the activation of synthesis of translesion polymerases.
    D. The destruction of LexA promotes synthesis of photolyase, which acts along with RecA to reverse the pyrimidine dimer formation process.
    Which one of the following options represents the combination of all correct statements?

(1) A and D (2) B and D
(3) A and C (4) C and D

The correct statements about the E. coli SOS response to DNA damage are:

• A. RecA-DNA filament complex stimulates the autoproteolytic activity of the LexA repressor.

• C. The SOS response includes the activation of synthesis of translesion polymerases.

Explanation:

• Statement A is correct. Upon DNA damage, RecA binds single-stranded DNA forming a nucleoprotein filament that acts as a coprotease, stimulating the self-cleavage (autoproteolysis) of the LexA repressor. This leads to derepression of SOS genes and induction of the DNA damage response.

• Statement B is incorrect. RecA is activated by binding to single-stranded DNA generated at stalled replication forks or DNA damage sites, not specifically by blunt ends of double-strand breaks.

• Statement C is correct. The SOS response induces the expression of specialized translesion synthesis (TLS) DNA polymerases (e.g., Pol II, Pol IV, Pol V) that allow replication to bypass DNA lesions.

• Statement D is incorrect. Photolyase is not part of the SOS regulon and does not require LexA destruction for its synthesis. Photolyase directly reverses UV-induced pyrimidine dimers using light energy and operates independently of RecA.

Correct option:

(3) A and C