By inhibiting replication, the large hepatitis delta antigen can indirectly regulate amber/W editing and its own expression.
Hepatitis delta virus (HDV) expresses two essential proteins with distinct functions. The small hepatitis delta antigen (HDAg-S) is expressed throughout replication and is needed to promote that process. The large form (HDAg-L) is farnesylated, is expressed only at later times via RNA editing of the amber/W site, and is required for virion assembly. When HDAg-L is artificially expressed at the onset of replication, it strongly inhibits replication. However, there is controversy concerning whether HDAg-L expressed naturally at later times as a consequence of editing and replication can similarly inhibit replication. Here, by stabilizing the predicted secondary structure downstream from the amber/W site, a replication-competent HDV mutant that exhibited levels of editing higher than those of the wild type was created. This mutant expressed elevated levels of HDAg-L early during replication, and at later times, its replication aborted prematurely. No further increase in amber/W editing was observed following the cessation of replication, indicating that editing was coupled to replication. A mutation in HDAg-L and a farnesyl transferase inhibitor were both used to abolish the ability of HDAg-L to inhibit replication. Such treatments rescued the replication defect of the overediting mutant, and even higher levels of amber/W editing resulted. It was concluded that when expressed naturally during replication, HDAg-L is able to inhibit replication and thereby inhibit amber/W editing and its own synthesis. In addition, the structure adjacent to the amber/W site is suboptimal for editing, and this creates a window of time in which replication can occur in the absence of HDAg-L.
Sato
Shuji
S
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111-1817, USA.
Cornillez-Ty
Cromwell
C
Lazinski
David W
DW
D002478:Cells, Cultured; D003062:Codon; D015967:Gene Expression Regulation, Viral; D003698:Hepatitis Delta Virus / Q000235:genetics / Q000502:physiology*; D035923:Hepatitis delta Antigens / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D016366:Open Reading Frames; D017393:RNA Editing; D012367:RNA, Viral / Q000737:chemistry; D014779:Virus Replication
D003062:Codon; D035923:Hepatitis delta Antigens; D012367:RNA, Viral; C442244:hepatitis delta virus large antigen