Specific defects in double-stranded DNA unwinding and homologous pairing of a mutant RecA protein

The DNA molecules bound to RecA filaments are extended 1.5-fold relative to B-form DNA, This extended DNA structure may be important in the recognitio n of homology between single-stranded DNA (ssDNA) and double-stranded DNA ( dsDNA). In this study, we show that the K286N mutation specifically impaire d the dsDNA unwinding and homologous pairing activities of RecA, without an apparent effect on dsDNA binding itself. In contrast, the R243Q mutation c aused defective dsDNA unwinding, due to the defective dsDNA binding of the C-terminal domain of RecA, These results provide new evidence that dsDNA un winding is essential to homology recognition between ssDNA and dsDNA during homologous pairing, (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.