RNA editing in hepatitis delta virus.

Hepatitis delta virus (HDV) relies heavily on host functions and on structural features of the viral RNA. A good example of this reliance is found in the process known as HDV RNA editing, which requires particular structural features in the HDV antigenome, and a host RNA editing enzyme, ADAR1. During replication, the adenosine at the amber/W site in the HDV antigenome is edited to inosine. As a result, the amber stop codon in the hepatitis delta antigen (HDAg) open reading frame is changed to a tryptophan codon and the reading frame is extended by 19 or 20 codons. Because these extra amino acids alter the functional properties of HDAg, this change serves a critical purpose in the HDV replication cycle. Analysis of the RNA secondary structures and regulation of editing in HDV genotypes I and III has indicated that although editing is essential for both genotypes, there are substantial differences. This review covers the mechanisms of RNA editing in the HDV replication cycle and the regulatory mechanisms by which HDV controls editing.