A ROLE FOR RNA-SYNTHESIS IN HOMOLOGOUS PAIRING EVENTS

The relationship between RNA synthesis and homologous pairing in vitro, catalyzed by RecA protein, was examined by using an established strand transfer assay system. When a short DNA duplex is mixed with single-stranded circles, RecA protein promotes the transfer of the minus strand of the duplex onto the complementary region of the plus-strand circle, with the displacement of the plus strand of the duplex. However, if minus-strand RNA is synthesized from the duplex pairing partner, joint molecules containing the RNA transcript, the plus strand of the DNA duplex, and the plus-strand circle are also observed to form. This reaction, which is dependent on RNA polymerase, sequence homology, and RecA protein, produces a joint molecule that can be dissolved by treatment with RNase H but not RNase A. Under these reaction conditions, product molecules form even when the length of shared homology between duplex and circle is reduced to 15 bp.