DNA Pairing and Strand Exchange by the Escherichia coli RecA and Yeast Rad51 Proteins without ATP Hydrolysis ON THE IMPORTANCE OF NOT GETTING STUCK*

The bacterial RecA protein and the homologous Rad51 protein in eukaryotes both bind to single-stranded DNA (ssDNA), align it with a homologous duplex, and pro-mote an extensive strand exchange between them. Both reactions have properties, including a tolerance of base analog substitutions that tend to eliminate major groove hydrogen bonding potential, that suggest a common mo-lecular process underlies the DNA strand exchange pro-moted by RecA and Rad51. However, optimal conditions for the DNA pairing and DNA strand exchange reactions promoted by the RecA and Rad51 proteins in vitro are substantially different. When conditions are optimized independently for both proteins, RecA promotes DNA pairing reactions with short oligonucleotides at a faster rate than Rad51. For both proteins, conditions that im