Hepatitis delta antigens enhance the ribozyme activities of hepatitis delta virus RNA in vivo

The mechanism of regulation for the ribozyme activity of hepatitis delta virus (HDV) RNA in infected cells is unknown. Previously, we developed a direct assay capable of detecting the ribozyme activity of HDV dimer or trimer RNAs in vivo (K.-S. Jeng, A, Daniel, and M. M. C, Lai, J, Virol, 70:2403-2410, 1996). In this study, we used this method to examine the effects of hepatitis delta antigen (HDAg) on the ribozyme activities of HDV RNA in vivo. The HDV multimer cDNAs were cotransfected with plasmids encoding either HDV small delta antigen (SHDAg) or large delta antigen (LHDAg), and the self-cleavage of the primary transcripts from the HDV cDNA was analyzed at day 2 posttransfection. The results were as follows. (i) Both HDAgs, particularly LHDAg, enhanced the self-cleavage activity of HDV RNA; however, HDAgs are not required for HDV RNA cleavage, (ii) HDAg could not restore the ribozyme activity of mutant HDV RNAs which have lost the ribozyme function, (iii) The enhancement of ribozyme activity by HDAg does not require HDV RNA replication. (iv) RNA-binding activity of HDAg is required for the enhancement of RNA cleavage. (v) The self-ligation activities of HDV ribozyme also were enhanced by HDAg. These results suggest that HDAg can regulate the cleavage and ligation of HDV RNA during the HDV life cycle.