Stimulation of Reca Protein Dependent Strand Assimilation and DNA Complex Formation by Single-Stranded DNA Binding Proteins

Abstract

RecA protein promotes the homology dependent hybridization of single-stranded DNA (ssDNA) with linear or circular duplex DNA (dsDNA) [strand-assimilatin]. Single-stranded DNA binding protein of E. coli (SSB) or the gene 32 protein of bacteriophage T4 stimulates the rate and extent of strand assimilation by a mechanism that does not appear to involve a recA protein. SSB complex. Furthermore, SSB stimulates pairing of circular ssDNA with RFII DNA indicating that free ends on the ssDNA partner are not necessary for SSB action. SSB also stimulates formation of recA protein-DNA complexes under conditions where it enhances strand assimilation, suggesting that these complexes are intermediates in the assimilation reaction. Finally, the recA629 mutant protein, which is cold labile for ssDNA annealing, promotes complex formation at 37°C, but not at 30°C, indicating that the mechanisms of strand pairing in assimilation and ssDNA annealing are closely related.