HOMOPOLYMER MUTATIONAL HOT-SPOTS MEDIATE HERPES-SIMPLEX VIRUS-RESISTANCE TO ACYCLOVIR

In the majority of cases, the mechanism underlying the resistance to a cyclovir (ACV) of herpes simplex viruses (HSVs) is thymidine kinase (T K) deficiency, Plaque isolates from eight ACV-resistant (ACV(r)) clini cal isolates from AIDS patients, of which five reactivated, were seque nced to determine the genetic lesion within the tk gene conferring res istance and whether this may have correlated with reactivation potenti al, Mutations were clustered within two homopolymer nucleotide stretch es, Three plaque isolates (1737-14, 90-150-3, and 89-650-5) had insert ion mutations within a stretch of 7 guanosines, while two isolates (89 -063-1 and 89-353-1) had frameshift mutations within a stretch of 6 cy tosines (a deletion and an insertion, respectively), Mutations resulte d in premature termination codons, and the predicted 28- and 32-kDa tr uncated TK products were detected by Western blot analysis of virus-in fected cell extracts, The repair of one homopolymer frameshift mutatio n (in isolate 1737-14) restored TK activity demonstrating that this mu tation is the basis of TK deficiency, Of the five reactivated isolates , four were TK deficient and contained frameshift mutations while the fifth retained TK activity because of its altered-TK or Pol(-) phenoty pe. These data demonstrate that the majority of ACV(r) clinical isolat es contain frameshift mutations within two long homopolymer nucleotide stretches which function as hot spots within the HSV tk gene and prod uce nonfunctional, truncated TK proteins.