Identification of a ribosome-binding site for a leader peptide encoded by Rous sarcoma virus RNA.

A new method for identifying ribosome-binding sites was developed to determine whether AUG codons in the 5'-terminal RNA sequence of Rous sarcoma virus were used to initiate protein synthesis. We found that when translation is inhibited, the major ribosome-binding site on Rous sarcoma virus RNA is at the 5'-proximal AUG codon, even though the primary translational product from this RNA, Pr76gag, is encoded behind the fourth AUG codon 331 bases downstream from the observed initiation site. These results suggest that ribosomes can initiate translation on Rous sarcoma virus RNA at more than one site, thereby producing a seven-amino-acid peptide, as well as the gag gene polyprotein precursor of Mr 76,000.