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Rescuing a sinking ship: The role of recombination gene products in SOS induction in Escherichia coli

In Escherichia coli (E. coli) DNA damage is repaired by the process of homologous recombination (HR). There are two main types of DNA damage, double-stranded (ds) DNA breaks (DSBs) and single-stranded (ss) DNA gaps (SSGs). DSBs can arise from external DNA-damaging agents, from induction of specific endonucleases which introduce DSBs in a specific recognition site, or due to endogenous DNA damage. SSGs are formed after replication of UV irradiated E. coli cells. Both types of DNA damage, DSBs and SSGs, induce the SOS response which includes elevated expression of genes whose products are involved in DNA metabolism, inhibition of cell division and prophage induction. DSBs are repaired by the RecBCD pathway of recombination, whereas SSGs are repaired by the RecF recombination pathway. Proteins in both recombinaton pathways, i.e., RecBCD and RecF, act to produce the recombinogenic RecA filament which is crucial for recombinational DNA repair and induction of the SOS response. It is known that the inactivation of some recombination gene products can lead to an impaired SOS response. Here we review the roles of recombination proteins in the formation of a RecA filament and in the induction of a SOS response.