Alterations in the recognition of nucleoside analogues as substrates by the deoxythymidine kinase of a 5-methoxymethyldeoxyuridine-resistant mutant of herpes simplex virus type 1.

Inhibition constants (Kis) were used as an estimate of the ability of various nucleoside analogues to be recognized as substrates by the deoxythymidine kinases (dTKs) of a 5-methoxymethyldeoxyuridine-resistant (MMdUr) mutant of herpes simplex virus type 1 (HSV-1) and its parent wild-type (wt). It was found that the Kis for the 5-position analogues MMdU, [E]-5-(2-bromovinyl)deoxyuridine, bromodeoxyuridine and iododeoxyuridine were increased approximately three-to fivefold, suggesting that they were poorer substrates for the MMdUr dTK than for the wt dTK. With the 2' analogues arabinosylthymine and 2' fluoro 5-methylarabinosyluracil, however, the Kis were increased to a much greater extent, 80- and 240-fold, respectively. These findings suggest that the resistance of the mutant MMdUr to these analogues may be due to a mutation(s) in the viral dTK that directly affects binding at the 2' recognition site and indirectly at the 5, while still allowing substantial activity with the natural substrate deoxythymidine.