Site-directed mutagenesis of herpes simplex virus type 1 thymidine kinase opposes the importance of amino acid positions 251, 321 and 348 for selective recognition of substrate analogs.

Seven site-directed mutants representing step-by-step transitions from the thymidine kinase (TK) of Herpes Simplex Virus type 1 (HSV 1) strain F to that one of strain SC16 were constructed, recombinantly produced and kinetically characterized in order to identify which of three differences in the amino acid sequence of these two TKs is/are responsible for their difference in substrate specificity. The preference of these two TKs for the substrate analogs aciclovir and ganciclovir was reported to be in reverse order (4.5), suggesting one of the amino acids in position 251 (cys or gly), 321 (ser or pro) and 348 (val or ile) of the HSV 1 wildtype TKs to be important for selective substrate recognition. However, the results of our study do not support this hypothesis.