ANALYSIS OF THE NONSENSE MUTANTS OF VARICELLA-ZOSTER VIRUS THYMIDINE KINASE

Three non-sense mutants of varicella-zoster virus (VZV) thymidine kina se (TK) gene, VZTK(325), VZTK(278) and VZTK(224), were isolated. The m utants had a single nucleotide substitution at codons 326, 279 and 225 , which changed the codon of TGG (tryptophan) to the stop codon TGA. T he wild type (WT) and mutant TKs were expressed in E. coli cells and t heir characteristics were evaluated. VZTK(224) lost TK activity, but V ZTK(325) and VZTK(278) maintained 74.8% and 21.2% of the WT TK activit y. On the other hand, all mutants lost the thymidylate kinase activity . Moreover, VZTK(325) and VZTK(278) polypeptides were heat-labile. The se data suggest that the carboxy-terminal portion of herpesvirus TK pl ays an important role in the stable folding of TK and thymidylate kina se activity.