Involvement of the activated form of RecA protein in SOS mutagenesis and stable DNA replication in Escherichia coli.

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Abstract
DNA damage activates RecA protein of Escherichia coli to a form (RecA*) that promotes proteolytic cleavage of LexA protein, the repressor of at least 17 DNA damage-inducible genes, resulting in expression of the SOS response. In addition to this known role, RecA* performs another function necessary for expression of SOS mutagenesis. The additional role of RecA* could be cleavage of another repressor, proteolytic processing of one or more proteins, or mechanistic interaction with DNA or with one or more other proteins. Experiments were designed to test the first possibility. The results suggest that neither SOS mutator activity nor UV mutagenesis requires induction by RecA* of any gene(s) outside the LexA regulon and that the additional role of RecA* is not cleavage of another repressor. Stable DNA replication, another DNA damage-inducible function, shares with SOS mutagenesis the requirement for RecA* activity, even in a strain constitutively expressing all LexA-controlled genes. In this strain, conditions that activate RecA initiate expression of stable DNA replication in the presence of chloramphenicol, without an intervening period of protein synthesis. The additional function of RecA* in stable DNA replication is probably not another antirepressor activity.