Internal entry of ribosomes and ribosomal scanning involved in hepatitis B virus P gene expression.

The recent demonstration that the synthesis of duck hepatitis B virus (HBV) reverse transcriptase does not require translational frameshifting and the finding that poliovirus mRNA translation occurs in a cap-independent manner by internal binding of ribosomes in the 5' noncoding region led us to design experiments to test the hypothesis of internal entry of ribosomes on C gene mRNA for HBV P gene expression. We show that in human cells, translation can be initiated at the first AUG of the HBV P gene by entry of ribosomes in a region located upstream of the P gene. Moreover, the leaky scanning of ribosomes observed on the first AUG of the HBV P gene could be responsible for the synthesis of the two forms of reverse transcriptase described for HBV particles.