Isolation and analysis of an aciclovir-resistant murine cytomegalovirus mutant.

An aciclovir (ACV)-resistant murine cytomegalovirus (MCMV) was isolated from the Smith strain and the mutant was analysed. Attempts were also made to identify directly the mutated gene. The 50% inhibitory concentration (IC(50)) of ACV for the mutant strain was approximately 30 times higher than that for the wild-type strain. The mutant strain was equally sensitive to ganciclovir (GCV), but slightly resistant to cidofovir (CDV) and foscarnet (PFA) when compared with the wild-type. Molecular analysis of the mutant strain revealed that a single base mutation of cytosine (C) to guanine (G) occurred at the 2476th nucleotide position in the DNA polymerase gene region, resulting in an amino acid substitution of proline (Pro) with alanine (Ala) at codon 826. The marker transfer experiment confirmed that this mutation conferred ACV resistance to MCMV. This mutation at codon 826 was easily identified by means of Hae III digestion of the selected PCR product and electrophoresis.