Cell cycle stage-specific phosphorylation of the Epstein-Barr virus immortalization protein EBNA-LP.
EBNA-LP is a viral nuclear oncoprotein implicated in the immortalization of B lymphocytes by Epstein-Barr virus. An analysis of EBNA-LP migration on polyacrylamide gels was performed with protein derived from the X50-7 lymphoblastoid cell line blocked by hydroxyurea or aphidicolin at the G1/S phase of the cell cycle or by nocodazole at the G2/M phase. More slowly migrating species of EBNA-LP were detected in G2/M phase-arrested cell extracts. Release from nocodazole G2/M block or treatment with phosphatase caused the more slowly migrating species of EBNA-LP to disappear. Analyses of 32PO(4)(3-)-labeled EBNA-LP protein immunoprecipitated from the drug-synchronized cells showed that phosphorylated EBNA-LP was present throughout the cell cycle but that phosphorylation increased in G2 and was maximal at G2/M. Phosphoamino acid analysis revealed that all phosphorylation was on serine residues only. The ability of EBNA-LP to be phosphorylated by p34(cdc2) kinase and casein kinase II exclusively on serines implicates these enzymes as being potentially involved in EBNA-LP phosphorylation.
Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pennsylvania 15261, USA.
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D001665:Binding Sites; D016203:CDC2 Protein Kinase / Q000378:metabolism; D047390:Casein Kinase II; D002453:Cell Cycle; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D019309:Epstein-Barr Virus Nuclear Antigens / Q000378:metabolism*; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D010449:Peptide Mapping; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014407:Tumor Cells, Cultured
D019309:Epstein-Barr Virus Nuclear Antigens; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase