THE BETA-PROTEIN OF PHAGE-LAMBDA BINDS PREFERENTIALLY TO AN INTERMEDIATE IN DNA RENATURATION

Phage lambda encodes two recombination proteins that are required for homologous recombination in a recA(-) host strain. Of these two recomb ination proteins, one is an exonuclease whose action on double-strande d DNA produces 3' single-stranded ends; the other, called beta protein , is a DNA binding protein that promotes the renaturation of complemen tary single strands. The enzymes of phage lambda provide a model for u nderstanding a recombination pathway called ''single-strand annealing' '. Further investigation of the binding of beta protein to DNA has rev ealed a new mechanism of renaturation. As reported before, beta protei n binds directly to single-stranded DNA, but not to double-stranded DN A. However, in the experiments reported here, we observed that beta pr otein bound more strongly to a presumed intermediate in the renaturati on reaction that beta itself catalyzed, and beta thereby protected all of a renatured duplex 83-mer oligonucleotide from nuclease digestion. (C) 1998 Academic Press Limited.