Tanaka S, Toh Y, Mori R
Department of Virology, School of Medicine, Kyushu University, Fukuoka, Japan.
Arch Virol. 1993;131(1-2):61-73. doi: 10.1007/BF01379080.
Thymidine kinase (TK) of herpes simplex virus (HSV) has been identified as one of the factors responsible for its virulence. We have previously isolated acyclovir (ACV)-resistant HSV type 2 (HSV-2), strain YS-4 C-1, by simple plaque cloning from a clinical isolate. Although YS-4 C-1 had extremely low TK activity, it retained high virulence in mice. To determine the mechanism of the reduction of TK activity, a molecular analysis of the YS-4 C-1 TK gene was performed. YS-4 C-1 produced TK mRNA, which was indistinguishable both in size and amount from that of wild-type strains. However, the YS-4 C-1 TK had a single amino acid change from serine to asparagine at amino acid residue 182 of the TK polypeptide, which was caused by a single nucleotide mutation. It was situated within a highly conserved region (162-194) and close to the putative nucleoside-binding site (169-177), one of the three active centers of TK. In order to confirm the effect of this missense mutation on both the TK activity and neurovirulence, the mutation was introduced into the TK genes of wild-type strains. Although all the recombinants were altered to ACV-resistant viruses with reduced TK activity, they retained high neurovirulence for mice. Our study thus suggested that this mutant TK, in spite of low activity, might play a role in the neurovirulence of HSV-2.
单纯疱疹病毒（HSV）的胸苷激酶（TK）已被确定为其毒力相关因素之一。我们之前通过从临床分离株中进行简单的噬斑克隆，分离出了对阿昔洛韦（ACV）耐药的2型单纯疱疹病毒（HSV-2），YS-4 C-1株。尽管YS-4 C-1的TK活性极低，但它在小鼠中仍保留高毒力。为了确定TK活性降低的机制，对YS-4 C-1的TK基因进行了分子分析。YS-4 C-1产生的TK mRNA在大小和数量上与野生型菌株的均无差异。然而，YS-4 C-1的TK在TK多肽的第182个氨基酸残基处有一个从丝氨酸到天冬酰胺的单氨基酸变化，这是由单个核苷酸突变引起的。它位于一个高度保守区域（162-194）内，且靠近假定的核苷结合位点（169-177），后者是TK的三个活性中心之一。为了证实这个错义突变对TK活性和神经毒力的影响，将该突变引入野生型菌株的TK基因中。尽管所有重组体都变成了具有降低的TK活性的ACV耐药病毒，但它们对小鼠仍保留高神经毒力。因此，我们的研究表明，这种突变的TK尽管活性低，但可能在HSV-2的神经毒力中起作用。
