Resistance of herpes simplex virus to acycloguanosine—genetic and physical analysis

Abstract

Resistance of herpes simplex viruses (HSV-1 and HSV-2) to acycloguanosine (ACG) is determined by the two genetic loci of HSV coding for deoxypyrimidine kinase (thymidine kinase) and DNA polymerase activity. Mutants of HSV-1 which induce defective deoxypyrimidine kinase (dPyK − mutants) activity can participate in interallelic complementation, and show variability in their resistance to acycloguanosine (ACG R). This allows for subdivision of dPyK − mutants based on their resistance to ACG. Mutants dPyK − and dPyK −11 are in one interallelic complementation group and both are 100-fold more resistant to ACG in a plaque reduction assay than is wild type herpes simplex virus type 1 (HSV-1). (The 50% inhibitory concentrations (ID 50) are 6.0 and 7.0 μM of ACG compared to 0.06 μM.) Mutant MDK (Kit) which cannot complement any other mutant is 500-fold more resistant to ACG (ID 50 = 50 μM). Other dPyK − mutants fall in between in their sensitivity to ACG. The map position of the mutations in the DNA polymerase locus which result in resistance to ACG ( acg r) was located by correlating the ACG sensitivity of HSV-1IHSV-2 intertypic combinants with restriction endonuclease analysis of their DNA. The mutations acg r and paa r (phosphonoacetic acid resistance) are contained in the same 1.3 kbp region of DNA (map units 40.2 to 41.0). The level of sensitivity to ACG is type specific, differing in HSV-1 and HSV-2. This type specificity is determined by DNA sequences within map units 39.6 to 41.0. Thus the DNA sequences for type-specific sensitivity and resistance to ACG are shown to be distinct and clustered in the same region as the HSV DNA polymerase locus.