Regulation of the SOS response and homologous recombination by an integrative and conjugative element

Integrative and conjugative elements (ICEs) are mobile genetic elements that transfer between bacteria and influence host physiology and promote evolution. ICE Bs1 of Bacillus subtilis modulates the host DNA damage response by reducing RecA filament formation. We found that the two ICE Bs1 -encoded proteins, RamT and RamA that modulate the SOS response in donors also function in recipient cells to inhibit both the SOS response and homologous recombination following transfer of the element. Expression of RamT and RamA caused a decrease in binding of the host single strand binding protein SsbA to ssDNA. We found that RamA interacted with PcrA, the host DNA translocase that functions to remove RecA from DNA, likely functioning to modulate the SOS response and recombination by stimulating PcrA activity. These findings reveal how ICE Bs1 can modulate key host processes, including the SOS response and homologous recombination, highlighting the complex interplay between mobile genetic elements and their bacterial hosts in adaptation and evolution.