cis rescue of a mutated reverse transcriptase gene of human hepatitis B virus by creation of an internal ATG.

Using mutational analysis, we have investigated the translation strategy of the reverse transcriptase gene (pol) of human hepatitis B virus. It has been proposed that this pol gene product is synthesized as a core-pol fusion protein from a polycistronic mRNA template via ribosomal frameshifting, a mechanism often seen in retroelements. Our data indicate that creation of a novel ATG initiation codon near the original ATG can compensate for a lethal missense mutation at the first ATG position of the pol open reading frame. Genetic analysis has rigorously ruled out the possibilities of frameshifting, non-ATG initiation, or RNA editing. These results are discussed in the context of a 5'-end entry model versus a novel model of direct internal entry of ribosomes.