SERINE-173 OF THE EPSTEIN-BARR-VIRUS ZEBRA PROTEIN IS REQUIRED FOR DNA-BINDING AND IS A TARGET FOR CASEIN KINASE-II PHOSPHORYLATION

An Epstein-Barr virus-encoded protein, ZEBRA, mediates the switch from latency to the viral lytic life cycle. ZEBRA's domain structure and D NA binding specificity resemble that of cellular transcriptional activ ators such as c-Fos/c-Jun. We show that ZEBRA, like c-Jun, is phosphor ylated by casein kinase II (CKII). The principal site of phosphorylati on is serine-173 (S173), five amino acids upstream of the basic DNA re cognition domain. CKII phosphorylation abrogated ZEBRA's capacity to b ind its target DNA sequences. S173 is a functional component of ZEBRA' s DNA binding domain, since mutation of S173 to alanine (S173A) reduce d DNA binding in vitro to 10% of wild-type levels. Transcriptional act ivation of a native viral promoter in vivo by mutant S173A was also re duced markedly. Reversible phosphorylation of S173 is likely to be an important means of regulating ZEBRA's activity in vivo.