FUNCTIONALLY IMPORTANT RESIDUES AT A SUBUNIT INTERFACE SITE IN THE RECA PROTEIN FROM ESCHERICHIA-COLI

Assembly of RecA subunits into long, helical oligomers is required for its roles in recombinational DNA repair and homologous genetic recomb ination. The crystal structure of RecA reveals an extensive network of amino acid residues that lie at the subunit boundaries. We have intro duced a large set of substitutions at 5 clustered residues, which are shown in the crystal structure to make specific contacts with position s in the neighboring monomer. We find that 3 of the 5 residues are imp ortant for RecA function (Lys216, Phe217, and Arg222), whereas the oth er 2 (Asn213 and Tyr218) are not. The patterns of functionally allowed substitutions provide insight into the chemical and steric constraint s required at these positions.