PHOSPHORYLATION OF HERPES-SIMPLEX VIRUS TYPE-1 US11 PROTEIN IS INDEPENDENT OF VIRAL GENOME EXPRESSION

The Us11 protein is a true late gene product of herpes simplex virus t ype 1 (HSV-1), whose exact function is unknown but which exhibits RNA- binding properties and which is phosphorylated on serine residues. In order to determine whether the Us11 protein is phosphorylated by cellu lar kinase(s) or by virally encoded kinase(s), the Us11 gene has been cloned and transiently expressed in HeLa cells. In addition, HeLa-deri ved cell lines have been selected for their ability to express Us11 pr otein constitutively. P-32-Labeling and analysis by two-dimensional el ectrophoresis of transiently and constitutively expressed Us11 protein demonstrated that, indeed, multiple phosphorylation of the protein oc curs in absence of HSV-1 genome expression, indicating that the protei n behaves as a natural substrate for cellular kinase(s). In addition, a sequence heterogeneity of the Us11 protein, due to a difference in t he number of SPREPR repeats, has been characterized between different strains of HSV-1.