HEPADNAVIRUS ASSEMBLY AND REVERSE TRANSCRIPTION REQUIRE A MULTICOMPONENT CHAPERONE COMPLEX WHICH IS INCORPORATED INTO NUCLEOCAPSIDS

Assembly of hepadnaviruses depends on the formation of a ribonucleopro tein (RNP) complex comprising the viral polymerase polypeptide and an RNA segment, epsilon, present on pregenomic RNA. This interaction, in turn, activates the reverse transcription reaction, which is primed by a tyrosine residue on the polymerase. We have shown recently that the formation of this RNP complex in an avian hepadnavirus, the duck hepa titis B virus, depends on cellular factors that include the heat shock protein 90 (Hsp90). We now report that RNP formation also requires AT P hydrolysis and the function of p23, a recently identified chaperone partner for Hsp90. Furthermore, we also provide evidence that the chap erone complex is incorporated into the viral nucleocapsids in a polyme rase-dependent reaction. Based on these findings, we propose a model f or hepadnavirus assembly and priming of viral DNA synthesis where a dy namic, energy-driven process, mediated by a multi-component chaperone complex consisting of Hsp90, p23 and, potentially, additional factors, maintains the reverse transcriptase in a specific conformation that i s competent for RNA packaging and protein priming of viral DNA synthes is.