Are pyrimidine dimers tolerated during DNA replication of UV-irradiated parvovirus minute-virus-of-mice in mouse fibroblasts?

The replication of the single-stranded DNA of parvovirus Minute-Virus-of-MIce (MVM) was depressed when virus was exposed to UV-light prior to infection of mouse fibroblasts. Most of the viral DNA containing pyrimidine dimers was permanently blocked in its conversion to double-stranded replicative forms (RF). Yet dimers might be tolerated to a low extent, considering that a minor fraction of parental RF molecules was sensitive to the action of the UV-specific endonuclease V of bacteriophage T4, UV-irradiation of the cells prior to infection with UV-damaged MVM increased the levels of both parental RF and total viral DNA synthesized. The sensitivity of parental RF molecules to the UV-specific endonuclease was little enhanced by preirradiation of the cells and did not appear to be sufficient to account for the stimulation of RF formation in those cultures. Since parvoviral single-stranded DNA is not a substrate for nucleotidyl excision repair, one interpretation of these results would be that the process(es) activated in preirradiated cells overcome(s) barriers to viral DNA replication other than elongation blocks at pyrimidine dimers. Alternatively, pyrimidine dimers tolerated in pretreated cultures might become protected from attack by the UV-endonuclease.