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Mol Cell Biol, April 1998, p. 1919-1926, Vol. 18, No. 4
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Hepatitis Delta Virus RNA Editing Is Highly Specific for the
Amber/W Site and Is Suppressed by Hepatitis Delta
Antigen
Andrew G.
Polson,1,
Herbert L.
Ley III,1
Brenda L.
Bass,1 and
John L.
Casey2,*
Department of Biochemistry and Howard Hughes
Medical Institute, University of Utah, Salt Lake City, Utah
84132,1 and
Division of Molecular
Virology and Immunology, Georgetown University Medical Center,
Rockville, Maryland 208522
Received 27 October 1997/Returned for modification 10 December
1997/Accepted 24 December 1997
RNA editing at adenosine 1012 (amber/W site) in the antigenomic RNA
of hepatitis delta virus (HDV) allows two essential forms of the viral
protein, hepatitis delta antigen (HDAg), to be synthesized from a
single open reading frame. Editing at the amber/W site is thought to be
catalyzed by one of the cellular enzymes known as adenosine deaminases
that act on RNA (ADARs). In vitro, the enzymes ADAR1 and ADAR2
deaminate adenosines within many different sequences of
base-paired RNA. Since promiscuous deamination could compromise the
viability of HDV, we wondered if additional deamination events occurred
within the highly base paired HDV RNA. By sequencing cDNAs derived from
HDV RNA from transfected Huh-7 cells, we determined that the RNA was
not extensively modified at other adenosines. Approximately 0.16 to
0.32 adenosines were modified per antigenome during 6 to 13 days posttransfection. Interestingly, all observed non-amber/W
adenosine modifications, which occurred mostly at positions that are
highly conserved among naturally occurring HDV isolates, were found in
RNAs that were also modified at the amber/W site. Such coordinate
modification likely limits potential deleterious effects of promiscuous
editing. Neither viral replication nor HDAg was required for the highly
specific editing observed in cells. However, HDAg was found to suppress
editing at the amber/W site when expressed at levels similar to those
found during HDV replication. These data suggest HDAg may regulate
amber/W site editing during virus replication.
*
Corresponding author. Mailing address: Division of
Molecular Virology and Immunology, Georgetown University Medical
Center, 5640 Fishers Lane, Rockville, MD 20852. Phone: (301) 881-2676. Fax: (301) 881-0810. E-mail: caseyj{at}medlib.georgetown.edu.

Present address: Department of Microbiology, University of San
Francisco Medical Center, San Francisco, CA 94143-0414.
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