HEPATITIS-DELTA VIRUS-RNA EDITING IS HIGHLY SPECIFIC FOR THE AMBER W SITE AND IS SUPPRESSED BY HEPATITIS-DELTA ANTIGEN/

RNA editing at adenosine 1012 (amber/W site) in the antigenomic RNA of hepatitis delta virus (HDV) allows two essential forms of the viral p rotein, hepatitis delta antigen (HDAg), to be synthesized from a singl e open reading frame, Editing at the amber/W site is thought to be cat alyzed by one of the cellular enzymes known as adenosine deaminases th at 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 wond ered if additional deamination events occurred within the highly base paired HDV RNA, By sequencing cDNAs derived from HDV RNA from transfec ted Huh-7 cells, we determined that the RNA was not extensively modifi ed at other adenosines. Approximately 0.16 to 0.32 adenosines were mod i fled per antigenome during 6 to 13 days posttransfection. Interestin gly, all observed non-amber/W adenosine modifications, which occurred mostly at positions that are highly conserved among naturally occurrin g HDV isolates, were found in RNAs that were also modified at the ambe r/W site, Such coordinate modification likely limits potential deleter ious effects of promiscuous editing, Neither viral replication nor HDA g was required for the highly specific editing observed in cells, Howe ver, HDAg was found to suppress editing at the amber/W site when expre ssed at levels similar to those found during HDV replication, These da ta suggest HDAg may regulate amber/W site editing during virus replica tion.