PHOSPHORYLATION OF THE TRANSLATIONAL REGULATOR, PHAS-I, BY PROTEIN-KINASE CK2

The primary site in PHAS-I for phosphorylation by protein kinase CK2 i n vitro was identified as Ser(111). A relatively small amount of phosp horylation of Ser(99) was also detected, and mutating Ser(99) to Ala i n PHAS-I slightly decreased phosphorylation by CK2 in vitro. In contra st, mutating Ser(111) to Ala almost abolished phosphorylation, confirm ing Ser(111) as the preferred site for CK2, Phosphorylation of Ser(111 ) did not decrease binding of PHAS-I to eIF4E, and results of peptide mapping experiments with PHAS-I immunoprecipitated from P-32-labeled a dipocytes indicated that Ser(111) was not phosphorylated in cells, The se results support the conclusion that CK2 is not involved in the cont rol of PHAS-I. (C) 1998 Federation of European Biochemical Societies.