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
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1-Phosphatidylinositol 4-Kinase
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Animals
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Antigen-Antibody Complex / analysis
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Antigens, Polyomavirus Transforming
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Antigens, Viral, Tumor / metabolism*
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Cell Line
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Fibroblasts / analysis
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Mice
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Mice, Inbred BALB C
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Oncogene Proteins, Viral / metabolism*
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Phosphoproteins / isolation & purification*
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Phosphoproteins / metabolism
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Phosphorylation
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Phosphotransferases / isolation & purification*
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Phosphotransferases / metabolism
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Phosphotyrosine
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Polyomavirus / immunology
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Polyomavirus / metabolism
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Protein-Tyrosine Kinases / metabolism
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Proto-Oncogene Proteins / metabolism*
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Proto-Oncogene Proteins pp60(c-src)
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Rats
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Tyrosine / analogs & derivatives
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Tyrosine / analysis
Substances
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Antigen-Antibody Complex
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Antigens, Polyomavirus Transforming
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Antigens, Viral, Tumor
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Oncogene Proteins, Viral
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Phosphoproteins
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Proto-Oncogene Proteins
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Phosphotyrosine
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Tyrosine
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Phosphotransferases
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1-Phosphatidylinositol 4-Kinase
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Protein-Tyrosine Kinases
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Proto-Oncogene Proteins pp60(c-src)