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SOS regulatory protein LexA LexA acts as a homodimer to repress a number of genes involved in the response to DNA damage (SOS response), including itself and RecA. RecA, in the presence of single-stranded DNA, acts as a co-protease to activate a latent autolytic protease activity (EC 3.4.21.88) of LexA, where the active site Ser is part of LexA. The autolytic cleavage site is an Ala-Gly bond in LexA (at position 84-85 in E. coli LexA; this sequence is replaced by Gly-Gly in Synechocystis). The cleavage leads to derepression of the SOS regulon and eventually to DNA repair. LexA in Bacillus subtilis is called DinR. LexA is much less broadly distributed than RecA. [DNA metabolism, DNA replication, recombination, and repair, Regulatory functions, DNA interactions]
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