The hepatitis B virus (HBV) P gene which encodes the reverse transcriptase and other proteins required for replication is expressed on the bicistronic mRNA pregenome which also encodes the capsid protein in its first cistron. Recent results have suggested that the hepadnaviral P gene is translated by internal entry of ribosomes upstream from the P gene, in the overlapping C gene. Using a reporter gene fused to the HBV C or P gene, we demonstrate that the C sequence does not allow internal initiation of translation. Alternatively, our results support a model in which the HBV P gene is translated by ribosomes which scan from the capped extremity of the bicistronic mRNA pregenome. The mechanism by which the ribosomes scan past four AUGs before they initiate translation at the P AUG was analyzed. Our results show that these AUGs are skipped via two mechanisms: leaky scanning on AUGs in a weak or suboptimal initiation context and translation of an out-of-C-frame minicistron followed by reinitiation at P AUG. The minicistron translation allows ribosomes to bypass an AUG in a favorable context that would otherwise be used as a start codon for translation of a truncated capsid protein. Our results suggest that this elaborated scanning mechanism permits the coordinate expression of the HBV C and P genes on the viral bicistronic mRNA pregenome.
The hepatitis B virus (HBV) e antigen (HBeAg) is a 15 kDa soluble antigen derived from a precursor protein (precore protein) by two processing events, cleavage of the N-terminal signal peptide and cleavage of the Cterminal 34 amino acids. So far, the role of the Cterminal sequences in secretion has not been analysed in full. In this study deletion of the last 60 amino acids was found to abrogate HBeAg secretion whereas deletions of the last 10, 25 or 39 amino acids decreased its secretion rate. These data demonstrate that C-terminal precore protein sequences are crucial for HBe secretion and determine its secretion rate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.