title: A small subclass of SV40 T antigen binds to the viral origin of replication.
abstract: We examined the affinities of SV40 large T antigen for unique viral DNA sequences by binding SV40 Bst NI DNA fragments in extracts of infected or transformed cells, and then immunoprecipitating the T antigen-DNA complex. The G fragment, which spans the viral origin of replication (ori) was quantitatively bound to T antigen. A T-antigen-specific monoclonal antibody (McI 7), which recognized only 5%-10% of the T antigen from infected or transformed cells, immunoprecipitated the majority of the ori-binding activity. This suggests that only a minor subclass of wild-type T antigen is active in binding to the origin. C6 cells contain a replication-defective mutant T antigen that when tested in the DNA-binding immunoassay, showed no affinity for the ori fragment. McI 7 not only failed to immunoprecipitate ori binding in C6 cells, but also did not detect any labeled C6 T antigen whatever. Thus McI 7 recognizes an immunologically distinct subset of wild-type 7 antigen that comprises the origin-binding form of the viral protein, which is absent in the C6 T antigen population. McI 122, which recognizes a 53 kilodalton host protein that complexes with T antigen, immunoprecipitated ori-binding activity from extracts of infected or transformed cells, but not from C6 cells. Thus wild-type T antigen can bind ori sequences even when complexed to the host protein. These data suggest that T antigen consists of different subpopulations with different functions.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology / Q000502:physiology*; D000957:Antigens, Viral, Tumor; D001483:Base Sequence; D002352:Carrier Proteins; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D004279:DNA, Viral / Q000502:physiology*; D004268:DNA-Binding Proteins; D013539:Simian virus 40 / Q000276:immunology* / Q000502:physiology; D014764:Viral Proteins / Q000502:physiology; D014779:Virus Replication
chemical_list: D000911:Antibodies, Monoclonal; D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D002352:Carrier Proteins; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D014764:Viral Proteins