INHIBITION OF HUMAN CYTOMEGALOVIRUS DNA MATURATION BY A BENZIMIDAZOLERIBONUCLEOSIDE IS MEDIATED THROUGH THE UL89 GENE-PRODUCT

2-Bromo-5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (BDCRB) is a member of a new class of benzimidazole ribonucleosides which inhibit human cytomegalovirus (HCMV) late in the replication cycle without inh ibiting viral DNA synthesis. We show here that polygenomic concatemeri c HCMV DNA does not mature to unit genome length in the presence of BD CRB. To discover the locus of action, virus resistant to BDCRB was sel ected hy serial passage in the presence of the compound. Genetic mappi ng experiments with BDCRB-resistant virus demonstrated that the resist ance phenotype mapped to one amino acid (Asp(344)Glu; low resistance) or two amino acids (Asp(344)Glu and Ala(355)Thr; high resistance) with in the product of exon 2 of the HCMV U(L)89 open reading frame. The HC MV U(L)89 open reading frame and its homologs are among the most conse rved open reading frames in the herpesviruses, and their products have sequence similarities to a known ATP-dependent endonuclease from the double-stranded DNA bacteriophage T4. These findings strongly suggest that BDCRB prevents viral DNA maturation by interacting with a U(L)89 gene product and that the U(L)89 open reading frame may encode an endo nucleolytic subunit of the putative HCMV terminase. Further, since mam malian cell DNA replication does not involve a DNA maturation step, co mpounds which inhibit viral DNA maturation should be selective and saf e.