engleski

The SOS response signalling mechanism: possible involvement of RecA loading activity

The SOS response involves many bacterial functions that are induced in response to damage of chromosomal DNA. The SOS response is regulated by the LexA repressor and the RecA nucleofilament which is formed at single stranded DNA. Such RecA nucleofilaments display a coprotease activity that stimulates self-cleavage of the LexA repressor. This cleavage enables transcription of more that 20 genes in the SOS pathway. Genetic analyses have shown that RecA and RecBCD are essential for SOS induction in response to double strand DNA breaks. In addition, it was shown that the SOS response is delayed in recFOR mutants. Interestingly, both enzymes, RecBCD and RecFOR, are involved in initiation of homologous recombination and both can load RecA protein on single strand DNA. We wanted to test our hypothesis that RecA loading activity is essential step in creating the SOS inducing signal. In order to test this, we measured SOS response in a strain in which the lacZ gene (expressing beta-galactosidase) is fused with the regulatory region of a sfiA SOS gene. We introduced additional mutations into this strain that inhibit RecA loading. To test whether different types of DNA damage require different enzyme processing, we measured SOS induction after UV and gamma irradiation, and introduction of double strand breaks by endonuclease.

SOS response; RecA protein; RecBCD enzyme; E. coli

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