An enhancer of recombination in polyomavirus DNA.

Previous work from this laboratory has indicated that intramolecular homologous recombination of polyomavirus (Py) DNA is dependent upon promoter structure or function. In this report, we demonstrate that Py DNA contains not two but three binding sites for transcription factor YY1, all located on the late side of viral origin of replication (ori) and the third well within the VP1 coding sequence. This third site (Y3), which may or may not play a role in transcription regulation, is immediately adjacent to a previously described recombination hot spot (S1/S2). We found that Py replicons carrying an altered Y3 site recombined in a manner suggesting partial inactivation of the S1/S hot spot. Point mutations precluding the binding of YY1 to Y3 in vitro depressed hot spot activity in vivo; however, of the two reciprocal products reflecting recombination at this spot, only that carrying the mutated Y3 site arose at a reduced rate. These results are interpreted in light of a model assuming that recombination occurs within a transcriptionally active viral chromatin tethered to the nuclear matrix by YY1.