COMPLEXES OF RECA PROTEIN IN SOLUTION - A STUDY BY SMALL-ANGLE NEUTRON-SCATTERING

RecA complexes on DNA and self-polymers were analysed by small-angle neutron scattering in solution. By Guinier analysis at small angles and by model analysis of a subsidiary peak at wider angles, we find that the filaments fall into two groups: the DNA complex in the presence of ATPγS, an open helix with pitch 95A °, a cross-sectional radius of gyration of 33A °and a mass per length of about six RecA units per turn, which corresponds to the state of active enzyme; and the compact form (bound to single-stranded DNA in the absence of ATP, or binding ATPγS in the absence of DNA, or just the protein on its own), a helical structure with pitch 70A °, cross-sectional radius of gyration 40A °and mass per length about five RecA units per turn, which corresponds to the conditions of inactive enzyme. The results are discussed in the perspective of unifying previous conflicting structural results obtained by electron microscopy. © 1990 Academic Press Limited.