RecA Protein Filaments Disassemble in the 5 to 3 Direction on

RecA protein forms filaments on both single- and dou-ble-stranded DNA. Several studies confirm that filament extension occurs in the 5 to 3 direction on single-stranded DNA. These filaments also disassemble in an end-dependent fashion, and several indirect observa-tions suggest that the disassembly occurs on the end opposite to that at which assembly occurs. By labeling the 5 end of single-stranded DNA with a segment of duplex DNA, we demonstrate unambiguously that RecA filaments disassemble uniquely in the 5 to 3 direction. The active form of the bacterial RecA protein is a filament formed on DNA. RecA has no known activities when it is not part of such a filamentous complex. Further, the action of several other bacterial proteins appears to be directed, at least in part, to the modulation of RecA filament assembly an