RECA-MEDIATED JOINT MOLECULE FORMATION BETWEEN O-METHYLATED RNA DNA HAIRPINS AND SINGLE-STRANDED TARGETS/

Chimeric oligonucleotides consisting of one DNA strand paired wits; an O-methylated RNA strand interrupted by six DNA residues have been use d in gene targeting experiments. Here we demonstrate that these hairpi ns can form a heteroduplex (or joint molecule) with single-stranded DN A targets in a reaction mediated by the E. coli RecA protein. One end of the double hairpin may unwind to form a 14-base-RecA filament which initiates the reaction. Chimeric oligonucleotides containing only O-m ethylated RNA residues on one strand or truncated hairpins lacking thi s 14-base segment did not participate in RecA-driven heteroduplex form ation under these reaction conditions. The results presented here repr esent a first step in studying one facet of a strategy which uses O-me thylated RNA residues as participants in homologous pairing events.