title: An 81 kd protein complexed with middle T antigen and pp60c-src: a possible phosphatidylinositol kinase.
abstract: It has previously been shown that a proportion of middle T antigen molecules exist in a stable complex with pp60c-src. Here we show that there appears to be a third component to the complex, a protein of molecular mass 81 kd (p81). p81 was phosphorylated exclusively on tyrosine residues in kinase assays performed using immunoprecipitates from polyoma virus-transformed cells and antibodies to both middle T and pp60c-src, and was also detected when immunoprecipitates were made from lysates of 32P-labeled cells. p81 was bound to middle T and pp60c-src in cell lines containing transforming mutants of middle T, but not (in phosphorylated form) to all nontransforming mutants. A parallel investigation of phosphatidylinositol kinase activity in immune complexes containing these middle T mutants revealed a complete coincidence between the presence of p81 and phosphatidylinositol kinase activity. We therefore suggest that p81 is a phosphatidylinositol kinase.
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D000936:Antigen-Antibody Complex / Q000032:analysis; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000378:metabolism*; D002460:Cell Line; D005347:Fibroblasts / Q000032:analysis; D051379:Mice; D008807:Mice, Inbred BALB C; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D010750:Phosphoproteins / Q000302:isolation & purification* / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000302:isolation & purification* / Q000378:metabolism; D019000:Phosphotyrosine; D011120:Polyomavirus / Q000276:immunology / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src); D051381:Rats; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
chemical_list: D000936:Antigen-Antibody Complex; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src)