title: Altered phosphorylation of free and bound forms of monkey p53 and simian virus 40 large T antigen during lytic infection.
abstract: We have identified the phosphorylation sites in monkey p53 as well as specific changes in the phosphorylation state of free and complexed forms of simian virus 40 (SV40) large T antigen (T) and monkey p53 isolate from SV40 lytically infected CV1 cells. Phosphopeptide analyses of free T and p53 (To and p53o) and complexed T and p53 (T+ and p53+) fractions indicated several quantitative increases in the specific phosphorylation of complexed forms of both proteins. The N terminus of monkey p53+ is phosphorylated at Ser-9, Ser-15, Ser-20, either Ser-33 or Ser-37, and at least one of Ser-90 to Ser-99. The C-terminal sites are Ser-315 and Ser-392. On comparing p53+ with p53o, we found that labeling of the two N-terminal phosphotryptic peptides encompassing residues 1 to 20 and 33 to 101 was increased fivefold and that Ser-315 was sevenfold more labeled than was Ser-392. When T+ was compared with To, the N-terminal peptide containing phosphorylation sites Ser-106 through Thr-124 was twofold more labeled, the peptide containing Ser-657 through Ser-679 was sixfold more labeled and contained up to four phosphorylated serine residues, and Ser-639 and Thr-701 appeared unchanged. Overall, T+ molecules appeared to contain 3.5 mol more of labeled phosphate than did To, with the N-terminal peptide appearing fully phosphorylated. The phosphopeptide patterns obtained for lytic T+ and To fractions were nearly identical to those found for wild-type SV40 T (stably complexed with mouse p53) and mutant 5080 T (defective for p53 binding) expressed in transformed C3H10T1/2 cells (L. Tack, C. Cartwright, J. Wright, A. Srinivasan, W. Eckhart, K. Peden, and J. Pipas, J. Virol. 63:3362-3367, 1989). These results indicate that increases in specific phosphorylation sites in both T+ and p53+ correlate with the association of T with p53. The enhanced phosphorylation state may be a consequence of complex formation between T and p53 or reflect an increased affinity of p53 for highly phosphorylated forms of T.
authors.affiliation: Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92138.
authors.forename: L C
authors.initials: LC
authors.lastname: Tack
authors.forename: J H
authors.initials: JH
authors.lastname: Wright
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D013539:Simian virus 40 / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism*; D014412:Tumor Virus Infections / Q000378:metabolism*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D046911:Macromolecular Substances; D010750:Phosphoproteins; D016159:Tumor Suppressor Protein p53