Genetic characteristics of new recA mutants of Escherichia coli K-12.

To search for functionally thermosensitive (FT) recA mutations, as well as mutations with differently affect RecA protein functions, seven new recA mutations in three different regions of the RecA protein structure proposed by Story et al. [R. M. Story, I. T. Weber, and T. A. Steitz, Nature (London) 355:318-325, 1992] were constructed. Additionally, the recA2283 allele responsible for the FT phenotype of the recA200 mutant was sequenced. Five single mutations (recA2277, recA2278, recA2283, recA2283E, and recA2284) and one double mutation (recA2278-5) generated, respectively, the amino acid substitutions L-277-->N, G-278-->P, L-283-->P, L-283-->E, I-284-->D, and G-278-->T plus V-275-->F in the alpha-helix H-beta-strand 9 region of the C-terminal domain of the RecA protein structure. According to recombination, repair, and SOS-inducible characteristics, these six mutations fall into four phenotypic classes: (i) an FT class, with either inhibition of all three analyzed functions at 42 degrees C (recA2283), preferable inhibition at 42 degrees C of recombination and the SOS response (recA2278), or inhibition at 42 degrees C of only recombination (recA2278-5); (ii) a moderately deficient class (recA2277); (iii) a nondeficient class (recA2283E); and (iv) a mutation with a null phenotype (recA2284). The recA2223 mutation generates an L-223-->M substitution in beta-strand 6 in a central domain of the RecA structure. This FT mutation shows preferable inhibition of the SOS response at 42 degrees C. The recA2183 mutation produces a K-183-->M substitution in alpha-helix F of the same domain. The Lys-183 position in the Escherichia coli RecA protein was found among positions which are important for interfilament interaction (R. M. Story, I. T. Weber, and T. A. Steitz, Nature (London) 355:318-325, 1992).