Unwinding of Duplex DNA in Complexes with recA Protein

The recA protein of Escherichia coli, which is involved in vivo in the complex events of recombination and SOS response, has manifold activities in vitro, e.g., adenosine triphosphate (ATP) hydrolysis, proteolytic activity on repressors, as well as strand assimilation, homologous pairing, and strand exchange on DNA (Craig and Roberts 1980; McEntee et al. 1980; West et al. 1981; Cunningham et al. 1981; for review, see Radding 1981). These functions are all dependent on the presence of DNA. recA protein has been purified (Weinstock et al. 1979; Ogawa et al. 1979; Roberts et al. 1979; Shibata et al. 1979) and has a molecular weight of 37,842, determined from the DNA sequence of the gene (Sancar et al. 1980). It has also been crystallized (McKay et al. 1980); the space group is P61, indicating a helix of six recA-protein monomers per unit cell. recA protein can also form filamentous aggregates in the...