RecA independent recombination of poly[d(GT)-d(CA)] in pBR322

Short sequence tracts composed of alternating guanosine and thymidine nucleotide residues poly[d(GT)-d(CA)] carried in a derivative of pBR322 were recombinogenic in a recA host. Recombination brought about by poly[d(GT)-d(CA)] tracts displayed two interesting properties: (i) the reaction was quasi-sequence-specific in that while recombination usually occurred between two poly[d(GT)-d(CA)] tracts, recombination also occurred between sequences bordering the dinucleotide repeats. (ii) recombination was enhanced when two poly[d(GT)-d(CA)] tracts were clustered within 250 base pairs of each other, but not when the repeats were separated by 3 kilobase pairs. The mechanism by which poly[d(GT)-d(CA)] stimulated recombination remains to be determined, but the behavior of these sequences is consistent with the idea that general recombination in E. coli may involve formation of Z-DNA.