A slow RecA protein, and its suppression in vivo

Abstract

A conserved (K/R)X(K/R) motif is found at the subunit‐subunit interfaces in bacterial RecA protein filaments. In the E. coli RecA protein, this motif is made up of residues K248 and K250. Both of these residues have a role in ATP hydrolysis (in trans across the interface) and in the transmission of conformational information across the interface. A K250R mutation creates a RecA protein that promotes both ATP hydrolysis and DNA strand exchange at a six‐fold lower rate than the wild type protein. E. coli strains overexpressing this mutant RecA protein also grow much slower than wild type strains. Suppressor mutations appear quickly, and most suppressor mutations inactivate RecA protein (leading to high levels of UV sensitivity). One suppressor mutation did not inactivate the RecA protein, but instead produced a recA variant that allowed normal rates of growth under normal growth conditions, while partially restoring UV resistance. The characteristics of this suppressor mutation and the purified mutant protein containing it will be reported.