%0 Journal Article %A Kato, Kentaro %A Yokoyama, Akihiko %A Tohya, Yukinobu %A Akashi, Hiroomi %A Nishiyama, Yukihiro %A Kawaguchi, Yasushi %T Identification of protein kinases responsible for phosphorylation of Epstein–Barr virus nuclear antigen leader protein at serine-35, which regulates its coactivator function %D 2003 %J Journal of General Virology, %V 84 %N 12 %P 3381-3392 %@ 1465-2099 %R https://doi.org/10.1099/vir.0.19454-0 %I Microbiology Society, %X Epstein–Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) is a phosphoprotein suggested to play important roles in EBV-induced immortalization. Earlier studies have shown that the major site of phosphorylation of EBNA-LP by cellular kinase(s) is a serine residue at position 35 (Ser-35) and that the phosphorylation of Ser-35 is critical for regulation of the coactivator function of EBNA-LP ( Yokoyama et al., J Virol 75, 5119–5128, 2001 ). In the present study, we have attempted to identify protein kinase(s) responsible for the phosphorylation of EBNA-LP at Ser-35. A purified chimeric protein consisting of glutathione S-transferase (GST) fused to a domain of EBNA-LP containing Ser-35 was found to be specifically phosphorylated by purified cdc2 in vitro, while GST fused to a mutated domain of EBNA-LP in which Ser-35 was replaced with alanine was not. In addition, overexpression of cdc2 in mammalian cells caused a significant increase in the phosphorylation of EBNA-LP, while this increased phosphorylation was eliminated if Ser-35 of EBNA-LP was replaced with alanine. These results indicate that the cellular protein kinase cdc2 mediates the phosphorylation of EBNA-LP at Ser-35. Recently, we reported that cdc2 and conserved protein kinases encoded by herpesviruses phosphorylate the same amino acid residue of target proteins ( Kawaguchi et al., J Virol 77, 2359–2368, 2003 ). Consistent with this, the EBV-encoded conserved protein kinase BGLF4 specifically mediated the phosphorylation of EBNA-LP at Ser-35. These results indicate that the coactivator function of EBNA-LP can be regulated by the activity of these cellular and viral protein kinases. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.19454-0