RUVA AND RUVB PROTEINS FACILITATE THE BYPASS OF HETEROLOGOUS DNA INSERTIONS DURING RECA PROTEIN-MEDIATED DNA STRAND EXCHANGE

RecA protein mediated DNA strand exchange between circular single stra nded DNA and linear duplex DNA readily bypasses short (up to 100 base pairs) heterologous inserts in one of the DNA substrates. Larger heter ologous inserts are bypassed with decreasing efficiency, and inserts l arger than 200 base pairs substantially block RecA-mediated DNA strand exchange. The RuvA and RuvB proteins dramatically facilitate the bypa ss of larger heterologous inserts. When the RuvA and RuvB proteins are added to an ongoing RecA protein-mediated strand exchange reaction, i nterior heterologous inserts of 1 kilobase pair are bypassed at signif icant frequencies. The RuvA, RuvB, and RecA proteins are all required for this activity. Bypass occurs only when homologous sequences are pr esent on both sides of the insert. When the heterologous insert is pos itioned at either end of the linear duplex substrate, the RuvA and Ruv B proteins do not significantly increase product formation in RecA pro tein-mediated DNA strand exchange reactions. The results suggest an im portant role for RuvA and RuvB in the bypass of DNA structural barrier s during recombinational DNA repair.