title: Middle T antigen as primary inducer of full expression of the phenotype of transformation by polyoma virus.
abstract: A large number of polyoma virus-transformed cells of rat, mouse, and hamster origin were examined for presence of T-antigen species. The results showed that all lines of cells contained middle and small T antigens, but not all contained a full-sized large T antigen, in some cell lines large T antigen was absent, whereas in others it was present as truncated forms lacking various lengths of the carboxy-terminal part of the protein. Cells transformed by the new viable deletion mutants of polyoma virus, dl-8 and dl-23, formed larger and smaller colonies or foci, respectively, when they were suspended in semisolid medium or plated as monolayers together with untransformed cells on a plastic surface. The deletions in the DNA of these mutants resulted in the shortening of the large and middle T antigens simultaneously without affecting the size of the small T antigen. Variation of large T-related proteins in dl-8 and dl-23-transformed cells seemed to be the same as that observed in wild-type-transformed cells. Regardless of the amount and size of large T-related protein in mutant-transformed cells, the phenotype of the cells was entirely dependent on the mutant used. The results suggest that (i) persistence of large T antigen is not universally required for the maintenance of the transformation phenotype, (ii) small T antigen alone may not be sufficient for inducing the full expression of the transformation phenotype, and (iii) middle T antigen is implicated as being primarily responsible for the full expression of the phenotype of transformation. The results also provide the evidence that the carboxy-terminal region of middle T antigen and a part of large T antigen are encoded in the genome in the same DNA segment around map units 88 to 94 in different reading frames.
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D000956:Antigens, Viral / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D000957:Antigens, Viral, Tumor; D001483:Base Sequence; D002460:Cell Line; D002472:Cell Transformation, Viral; D002874:Chromosome Mapping; D006224:Cricetinae; D004591:Electrophoresis, Polyacrylamide Gel; D005814:Genes, Viral; D051379:Mice; D009154:Mutation; D010446:Peptide Fragments / Q000032:analysis; D010641:Phenotype; D011120:Polyomavirus / Q000235:genetics / Q000276:immunology*; D051381:Rats; D013696:Temperature
chemical_list: D000951:Antigens, Neoplasm; D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D010446:Peptide Fragments