Abstract
The polypeptides of polyoma and SV40 virions are phosphorylated. An estimate of the amount of phosphorylation of the major virus capsid protein (VP1) has been made using two-dimensional gel electrophoresis to resolve phosphorylated from non-phosphorylated forms. The results suggest that in both polyoma and SV40 virions about 12% of VP1 molecules are phosphorylated. In unassembled VP1 molecules immunoprecipitated from extracts of infected cells the proportion is greater, about 33%. The possibility that phosphorylated VP1 may form the penton proteins of the virus capsid is discussed.