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

Rml is a chimeric DNA molecule consisting of a polyoma genome in which a pa rtly duplicated VP1-coding region brackets an insert of murine DNA (Ins); w hen transfected into mouse cells, Rml recombines intramolecularly to yield infectious, unit-length, polyoma DNA. We report here that Rml encodes a pol ypeptide 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 Vm P1-coding sequence strongly reduces the ability of Rml to yield polyoma DNA . In contrast, mutating the portion of the VP1-coding sequence which is not part of the VmP1-coding sequence has little or no impact on the ability of Rml to yield polyoma DNA, even though it renders such DNA noninfectious. T hus, release of polyoma DNA from Rml involves a function of VP1 distinct fr om that ensuring virus assembly and propagation; since VP1 can arise only a fter recombination has occurred, VmP1, but not VP1, could carry such a func tion. We suggest that VmP1 acts in concert with VP2, which we have already reported to stimulate recombination in Rml. (C) 2001 Academic Press.