Analysis of the non-sense mutants of varicella-zoster virus thymidine kinase

Summary

Three non-sense mutants of varicella-zoster virus (VZV) thymidine kinase (TK) gene, VZTK₃₂₅, VZTK₂₇₈ and VZTK₂₂₄, were isolated. The mutants had a single nucleotide substitution at codons 326, 279 and 225, which changed the codon of TGG (tryptophan) to the stop codon TGA. The wild type (WT) and mutant TKs were expressed in E. coli cells and their characteristics were evaluated. VZTK₂₂₄ lost TK activity, but VZTK₃₂₅ and VZTK₂₇₈ maintained 74.8% and 21.2% of the WT TK activity. On the other hand, all mutants lost the thymidylate kinase activity. Moreover, VZTK₃₂₅ and VZTK₂₇₈ polypeptides were heat-labile. These data suggest that the carboxy-terminal portion of herpesvirus TK plays an important role in the stable folding of TK and thymidylate kinase activity.