AN ENHANCER OF RECOMBINATION IN POLYOMAVIRUS DNA

Previous work from this laboratory has indicated that intramolecular h omologous recombination of polyomavirus (Py) DNA is dependent upon pro moter structure or function. In this report, we demonstrate that Py DN A contains not two but three binding sites for transcription factor YY 1, all located on the late side of viral origin of replication (ori) a nd the third well within the VP1 coding sequence, This third site (Y3) , which may or may not play a role in transcription regulation, is imm ediately adjacent to a previously described recombination hot spot (S- 1/S-2). We found that Py replicons carrying an altered Y3 site recombi ned in a manner suggesting partial inactivation of the S-1/S-2 hot spo t. Point mutations precluding the binding of YY1 to Y3 in vitro depres sed hat 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 lig ht of a model assuming that recombination occurs within a transcriptio nally active viral chromatin tethered to the nuclear matrix by YY1.