A mutation increasing the size of the polyoma virion proteins, VP2 and VP3

The ts48 mutant of polyoma virus carries a temperature-sensitive mutation (tsA) which affects the polyoma large T antigen, blocking viral DNA synthesis at the nonpermissive temperature. In addition, there are at least two other changes in the ts48 genome which affect virus-coded proteins. There is a single base change which abolishes an HpaII restriction enzyme cleavage site in the portion of the early region coding simultaneously for the polyoma medium and large T antigens. There is also a single base change in the late region of the genome which results in the synthesis of virion proteins, VP2 and VP3, larger than the corresponding wild type proteins. The change in the late region abolishes the normal termination codon for VP2 and VP3.