Targeting in linear DNA duplexes with two complementary probe strands for hybrid stability.

A new in vitro hybridization reaction targets two short complementary RecA protein-coated DNA probes to homologous sequences at any position in a linear duplex DNA molecule. Stable hybrids are obtained after RecA protein removal when both complementary probe strands are present in a four-stranded hybrid, but not when one probe strand is present in a three-stranded hybrid. In four-stranded hybrids with one probe strand biotinylated and the other radiolabelled, the deproteinized hybrids can be isolated and detected by affinity capture on streptavidin-coated magnetic beads. RecA-mediated targeting of complementary biotinylated DNA probe strands allows the affinity capture of 48.5-kilobase duplex lambda genomic DNA. These reactions provide a means of isolating any desired duplex gene or chromosomal DNA fragment.