The packaging signal in hepatitis B virus pregenome functions only at the 5' end

When the hepatitis B virus (HBV) replicates, a full-size transcript of the viral genome, called pregenome RNA, is made and is selectively packaged into virus core particles. This selective encapsidation is dependent upon the presence of a specific cis-acting sequence called the packaging signal that is found at the 5' end of the pregenome RNA. Deletion analysis revealed that this packaging signal was located in a 70 bp stretch of nucleotides. Packaging defective virus genome containing the 70 bp packaging signal sequence at several locations, showed that the packaging occurs effectively only when the signal is located near the 5' end of the pregenome RNA. Packaging also occurred with a 2.4 kb viral RNA whose 5' region sequence was different from that of the pregenome RNA, but which has the packaging signal sequence inserted at the 5' region.