A HOST FACTOR THAT BINDS NEAR THE TERMINI OF HEPATITIS-B VIRUS PREGENOMIC RNA

The terminal regions of hepatitis B virus (HBV) pregenomic RNA (pgRNA) harbors sites governing many essential functions in the viral life cy cle, including polyadenylation, translation, RNA encapsidation, and DN A synthesis. We have examined the binding of host proteins to a 170-nu cleotide region from the 5' end of HBV pgRNA; a large portion of this region is duplicated at the 3' end of this terminally redundant RNA. B y UV cross-linking labeled RNA to HepG2 cell extracts, we have identif ied a 65-kDa factor (p65) of nuclear origin which can specifically bin d to this region. Two discrete binding sites were identified within th is region; in vitro cross-competition experiments suggest that the sam e factor hinds to both elements. One binding site (termed UBS) overlap s a portion of the highly conserved stem-loop structure (epsilon), whi le the other site (termed DBS) maps 35 nucleotides downstream of the h exanucleotide polyadenylation sequence. Both binding sites are highly pyrimidine rich and map to regions previously found to be important in the regulation of viral polyadenylation. However, functional analysis of mutant binding sites in vivo indicates that p65 is not involved in the polyadenylation of HBV pgRNA, Potential roles for the factor in v iral replication in vivo are discussed.