Hepadnaviral assembly is initiated by polymerase binding to the encapsidation signal in the viral RNA genome.

Abstract

Hepadnaviruses, as well as other pararetroviruses, express their pol (P) gene product unfused to the preceding core gene implying that these retroelements have developed a mechanism for initiating assembly and replication that is principally different from the one used by retroviruses and retrotransposons. We have analysed this mechanism for the human hepatitis B virus by using a newly developed, highly sensitive detection method based upon radiolabelling of the P protein at newly introduced target sites for protein kinase A. The results obtained demonstrate that polymerase encapsidation depends on the concommnittant encapsidation of the HBV RNA pregenome and that packaging of the viral RNA, in turn, depends on the presence of P protein. Loss of P protein encapsidation by mutations inactivating the HBV RNA encapsidation signal E could be compensated by trans-complementation with recombinant RNA molecules carrying the E sequence. Thus, in contrast to retroviral replication, the interaction of the hepadnaviral P protein and the RNA genome at its packaging signal appears to be crucial for initiating the formation of replication-competent nucleocapsids. Furthermore, RNA control of P protein packaging stringently limits the number of polymerase molecules that can be encapsidated.

Dominant negative mutants of the duck hepatitis B virus core protein interfere with RNA pregenome packaging and viral DNA synthesis

“…Figure 2A illustrates that in the total RNA preparations, both the RNA pregenome transcribed from DHBV HTD (arrow) and the mRNAs of the respective mutants (additional bands), can be detected by this method. As expected, in the nucleocapsid preparations, only the RNA pregenome and traces of the P269 and S163 transcripts can be seen, because P269 and S163, but not C119 and DcGFP, encode the hepadnaviral encapsidation signal e. 22 A comparison of total and encapsidated pregenomic RNA shows that P269 and S163, but not C119 and DcGFP, markedly interfered with RNA pregenome packaging. These results were confirmed by an analogous Northern blot analysis of mutants P269, C119, and DcGFP (data not illustrated).…”

Molecular and Cellular Biology

“…4). The poor activity of this novel promoter is in accordance with the assumption that only a single Pol polypeptide per virion is encapsidated (2), as opposed to the core protein, for which about 240 polypeptides are required (4). The low level of this putative transcript might be the reason why so far it has escaped detection by the conventional RNA analysis tools.…”

Serological and molecular epidemiological outcomes after two decades of universal infant hepatitis B virus (HBV) vaccination in Nunavut, Canada

“…To produce viral progeny, pregenomic mRNA must be encapsidated by viral core protein, which self-assemble into the nucleocapsid once the viral polymerase binds a secondary stem-loop structure, epsilon, on the pregenomic mRNA [43][44][45][46]. Once attached to epsilon, the viral polymerase will begin to produce the genomic negative-sense strand by reverse transcriptase functionality within the immature core particle.…”