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J Virol, June 1998, p. 4721-4728, Vol. 72, No. 6
Department of Biologic and Materials
Sciences,
Received 26 November 1997/Accepted 4 March 1998
2,5,6-Trichloro-1-
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Resistance of Human Cytomegalovirus to
Benzimidazole Ribonucleosides Maps to Two Open Reading Frames: UL89
and UL56

-D-ribofuranosyl benzimidazole
(TCRB) is a potent and selective inhibitor of human cytomegalovirus
(HCMV) replication. TCRB acts via a novel mechanism involving
inhibition of viral DNA processing and packaging. Resistance to the
2-bromo analog (BDCRB) has been mapped to the UL89 open reading frame (ORF), and this gene product was proposed as the viral target of the
benzimidazole nucleosides. In this study, we report the independent
isolation of virus that is 20- to 30-fold resistant to TCRB (isolate
C4) and the characterization of the virus. The six ORFs known to be
essential for viral DNA cleavage and packaging (UL51, UL52, UL56, UL77,
UL89, and UL104) were sequenced from wild-type HCMV, strain Towne, and
from isolate C4. Mutations were identified in UL89 (D344E) and in UL56
(Q204R). The mutation in UL89 was identical to that previously reported
for virus resistant to BDCRB, but the mutation in UL56 is novel. Marker
transfer analysis demonstrated that each of these mutations
individually caused ~10-fold resistance to the benzimidazoles and
that the combination of both mutations caused ~30-fold resistance.
The rate and extent of replication of the mutants was the same as for
wild-type virus, but the viruses were less sensitive to inhibition of
DNA cleavage by TCRB. Mapping of resistance to UL56 supports and
extends recent work showing that UL56 codes for a packaging motif
binding protein which also has specific nuclease activity (E. Bogner et
al., J. Virol. 72:2259-2264, 1998). Resistance which maps to two
different genes suggests that their putative proteins interact and/or
that either or both have a benzimidazole ribonucleoside binding site. The results also suggest that the gene products of UL89 and UL56 may be
antiviral drug targets.
*
Corresponding author. Mailing address: School of
Dentistry, University of Michigan, Ann Arbor, MI 48109-1078. Phone:
(734) 763-5579. Fax: (734) 764-7406. E-mail:
jcdrach{at}umich.edu.
Present address: Division of AIDS, National Institute of Allergy
and Infectious Diseases, National Institutes of Health, Bethesda, MD
20892.
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