FORMATION OF BASE TRIPLETS BY NON-WATSON-CRICK BONDS MEDIATES HOMOLOGOUS RECOGNITION IN RECA RECOMBINATION FILAMENTS

Whereas complementary strands of DNA recognize one another by forming Watson-Crick base pairs, the way in which RecA protein enables a singl e strand to recognize homology in duplex DNA has remained unknown. Rec ent experiments, however, have shown that a single plus strand in the RecA filament can recognize an identical plus strand via bonds that, b y definition, are non-Watson-Crick, In experiments reported here, base substitutions had the same qualitative and quantitative effects on th e pairing of two identical strands in the RecA filament as on the reco gnition of duplex DNA by a third strand, indicating that similar non-W atson-Crick interactions govern both reactions.