Mechanistic insights into the structure and function of the RecA C-terminal tail.

Bacterial RecA protein oligomerizes on single-stranded DNA (ssDNA) in the presence of ATP to form an active filament, RecA*, which is essential for homologous recombination and the activation of bacterial DNA damage response (SOS response). Despite extensive studies on the structure and function of RecA and RecA*, the exact function of the RecA flexible C-terminal tail remains poorly understood. Here, we report the crystal structure of the full-length RecA protein from K. pneumoniae, revealing that the C-terminal tail adopts a β-strand conformation. The negatively charged C-terminal tail is observed to interact with two positively charged conserved residues in the RecA core ATPase domain. We also demonstrate that the C-terminal tail of the E. coli and K. pneumoniae RecA inhibits the formation of RecA filament, DNA binding, and DNA strand exchange during homologous recombination, but promotes LexA self-cleavage as a co-protease and enhances the SOS response induced by mitomycin and ciprofloxacin. Our results provide mechanistic insights into the regulatory function of the RecA C-terminal tail in genome maintenance and DNA damage response.