The gene encoding the major viral structural protein stimulates recombination in polyomavirus DNA.

RmI is a chimeric DNA molecule consisting of a polyoma genome in which a partly duplicated VP1-coding region brackets an insert of murine DNA (Ins); when transfected into mouse cells, RmI recombines intramolecularly to yield infectious, unit-length, polyoma DNA. We report here that RmI encodes a polypeptide of 337 amino acids (designated VmP1) which includes the N-terminal 328 amino acids of VP1 and 9 amino acids specified by Ins. Mutating the VmP1-coding sequence strongly reduces the ability of RmI to yield polyoma DNA.

Involvement of minor structural proteins in recombination of polyoma virus DNA.

We have previously observed that a polyoma-mouse chimeric DNA molecule (RmI) in which the murine DNA insert is flanked by directly repeated viral sequences is effectively converted into unit-length polyoma DNA upon transfection of permissive mouse cells. This intramolecular recombination event appears to be dependent on VmP1, a protein encoded by RmI which includes the 328 N-terminal amino acids of polyoma VP1, and nine amino acids of murine origin carrying the C-terminus of the protein. We report here that introducing mutations into the VP2/VP3 coding sequence reduces the ability of RmI to generate polyoma DNA, even though the same mutations seem to exert little or no effect on the ability of polyoma DNA to either replicate or accumulate inside transfected cells.

Rescue of polyomavirus DNA after co-transfection of recombinant plasmids with viral DNA fragments.

Plasmid DNA bearing a single copy of the mouse polyomavirus (Py) genome (template A) was transfected into murine cells together with another DNA (template B) carrying intact the viral sequence interrupted in template A. Rescue of unit-length Py DNA including markers from both templates was observed as long as the viral DNA in B overlapped that split in A by one kbp or more. Such rescue was not detectably enhanced by linearizing either or both template(s), and occurred in the absence of template replication.

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).