Measurements of the molecular size of the simian virus 40 large T antigen

Abstract

A measure of the MW of the large SV-40 T antigen was sought by SDS[sodium dodecyl sulfate]-polyacrylamide gel electrophoresis, random-coil chromatography and sedimentation-velocity analysis in a density gradient. Large T antigen obtained from a SV-40-transformed human [fibroblast] cell line either by immunoprecipitation or by standard preparatory methods migrated like at 94,000 MW weight ($ 94 k) polypeptide in SDS-gels but was found to have an approximate MW of 75,000 (.+-. 7%) by the other 2 methods. Comparable results were observed with T antigen obtained from lytically infected [African green] monkey [kidney] cells. In view of the strong theoretical basis for the guanidine method and the agreement with the sedimentation data, these findings suggest that the MW of this protein is $ 75-80K as opposed to 94-100K and, therefore, that considerably less than the entire early region of SV-40 is required to encode it. This size estimate is in keeping with earlier results which revealed a normal-size T antigen in cells infected with viable deletion mutants lacking as much as 10% of the early region.