title: Mapping of the amino-terminal half of polyomavirus middle-T antigen indicates that this region is the binding domain for pp60c-src.
abstract: The majority of the carboxy-terminal half of polyomavirus middle-T antigen has been variously mutated and, with the exception of the putative membrane-binding domain (amino acids 394 to 415), was found to be largely dispensible for the transforming activity of the protein. A comparison of the small-T antigen amino acid sequences (equivalent to the region of middle-T encoded by exon 1) of simian virus 40, BK virus, polyomavirus, and a recently described hamster papovavirus highlighted regions of potential interest in mapping functions to the amino-terminal half of polyomavirus middle-T antigen. The regions of interest include amino acids 168 to 191 (previously investigated by this group [S. H. Cheng, W. Markland, A. F. Markham, and A. E. Smith, EMBO J. 5:325-334, 1986]), two cysteine-rich clusters (amino acids 120 to 125 and 148 to 153), and amino acids 92 to 117 (within the limits of the previously described hr-t mutant, SD15). Point mutations, multiple point mutations, and deletions were made by site-specific and site-directed mutagenesis within the cysteine-rich clusters and residues 92 to 117. Studies of the transforming ability of the altered middle-T species demonstrated that this activity is highly sensitive to amino acid changes. All four regions (as defined above) within the amino-terminal half of middle-T have now been studied in detail. The phenotype of the mutants is predominantly transformation defective, and the corresponding variant middle-T species are characterized by being either totally or severely handicapped in the ability to associate actively with pp60c-src. Whether the mutations affect the regions of interaction between middle-T and pp60c-src or simply interfere with the overall conformation of this domain is not known. However, there would appear to be a conformational constraint on this portion of the molecule with regard to its interaction with pp60c-src and by extension to the ability of the middle-T species to transform.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D002872:Chromosome Deletion; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D010957:Plasmids; D011120:Polyomavirus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src); D051381:Rats; D013447:Sulfites / Q000494:pharmacology
chemical_list: D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D013447:Sulfites; D016392:Proto-Oncogene Proteins pp60(c-src)