title: Differential subcellular localization of in vivo-phosphorylated and nonphosphorylated middle-sized tumor antigen of polyoma virus and its relationship to middle-sized tumor antigen phosphorylating activity in vitro.
abstract: A small fraction of polyoma virus middle-sized tumor (T) antigen is phosphorylated in vivo, resulting in a small amount of phosphotyrosine and phosphothreonine and significantly larger amounts of phosphoserine. When infected cells are separated into nuclear, plasma membrane, and low-speed supernatant fractions, 80-95% of in vivo-phosphorylated middle-sized T antigen is localized to the plasma membrane fraction, while 25-50% of [35S]methionine-labeled middle-sized T antigen is found in the nuclear fraction and the same amount is found in the plasma membrane fraction. Immunoprecipitated T antigens contain a protein kinase activity that phosphorylates middle-sized T antigen at tyrosine residues. Eighty to 90% of this activity is located in the plasma membrane fraction. When immunoprecipitated T antigens are treated with alkaline phosphatase, middle-sized T antigen-phosphorylating activity decreases as 32PO4 is lost from in vivo 32P-labeled middle-sized T antigen. The possibility that in vivo-phosphorylated middle-sized T antigen located in the plasma membrane is an active tyrosine-specific kinase is discussed.
mesh_terms: D000469:Alkaline Phosphatase; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000956:Antigens, Viral / Q000032:analysis* / Q000302:isolation & purification; D000957:Antigens, Viral, Tumor; D002478:Cells, Cultured; D051379:Mice; D008970:Molecular Weight; D010766:Phosphorylation; D011120:Polyomavirus / Q000201:enzymology / Q000276:immunology*; D011494:Protein Kinases / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D011494:Protein Kinases; D000469:Alkaline Phosphatase