Phosphorylation and nuclear localization of the varicella-zoster virus gene 63 protein

The protein encoded by varicella-zoster virus open reading frame 63 and carboxy-terminal deletions of the same were expressed either as fusion proteins at the carboxy terminus of the maltose-binding protein in Escherichia coli or independently in transfected mammalian cells. The truncations contained amino acids 1 to 142 (63ΔN) or 1 to 210 (63ΔK) of the complete 278-amino-acid primary sequence. Recombinant casein kinase II phosphorylated the 63F and 63ΔKF fusion proteins in vitro but did not phosphorylate the 63ΔNF fusion protein, implying that phosphorylation occurred between amino acids 142 and 210. Immunoprecipitation of ³⁵S- or ³²P-labelled extracts of cells transfected with plasmids expressing 63, 63ΔN, or 63ΔK also indicated that in situ phosphorylation most likely occurred between amino acids 142 and 210. These combined results suggest that casein kinase II plays a significant role in the phosphorylation of the varicella-zoster virus 63 protein. Indirect immunofluorescence of transfected cells indicated nuclear localization of the 63 protein and cytoplasmic localization of 63ΔK and 63ΔN, implying a requirement for sequences between amino acids 210 and 278 for efficient nuclear localization.