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

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Abstract
A measure of the molecular weight of the large simian virus 40 T antigen was sought by SDS-polyacrylamide gel electrophoresis, random-coil chromatography, and sedimentation-velocity analysis in a density gradient. Large T antigen obtained from a simian virus 40-transformed human cell line either by immunoprecipitation or by standard preparatory methods migrated like a 94,000-molecular-weight (approximately 94K) polypeptide in SDS-gels but was found to have an approximate was observed with T antigen obtained from lytically infected monkey cells. In view of the strong theoretical basis for the guanidine method and the agreement with the sedimentation data, these findings suggest that the molecular weight of this protein is approximately 75 to 80K as opposed to 94 to 100K and, therefore, that considerably less than the entire early region of simian virus 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.