engleski

The efficiency of DNA repair in ssb-1 mutant: SSB is actively replaced with RecA by RecFOR

Single-stranded DNA binding (SSB) protein is an essential protein because of its role in DNA replication, recombination and DNA repair. SSB stimulates the RecA filament formation and subsequent exchange of DNA strands. To produce RecA filament, the SSB protein (bound to ssDNA) is replaced with RecA protein through the action of RecFOR proteins. Alternatively, the recombinogenic filament can be produced through the RecA loading mediated by the RecBCD enzyme, and this process does not require the replacement of SSB with RecA. In this study we wanted to test whether the replacement of SSB with RecA is an essential feature of the mechanism for the recombinogenic filament formation by RecFOR proteins. To address this question we studied the thermosensitive mutant ssb-1 and its derivatives. The ssb1 mutant is UV sensitive and is blocked in DNA replication. Biochemically, the SSB-1 protein has decreased stability of the tetrameric structure, and has decreased ssDNA-binding affinity. We found that viability is severely decreased in ssb-1 recB1080 double mutant at 42°C. However, DNA repair is more efficient in ssb-1 recB1080 double mutant than in ssb-1 single mutant at 42°C. These observations led us to the conclusion that replacement of SSB protein with RecA protein is an essential feature of the mechanism for RecA filament formation through the action of RecFOR proteins.

ssb; RecFOR; RecA loading; E. coli

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