Formation of ribosome-RNA initiation complexes with alfalfa mosaic virus RNA 4 and RNA 3

Abstract

RNA 4 of alfalfa mosaic virus (AMV) is a monocistronic messenger for the coat protein. We have determined the sequence of the 40±2 nucleotides in RNA 4 that were protected in the initiation complex formed with wheat germ 80 S ribosomes from digestion by T1 or pancreatic ribonucleases. The AUG coat protein initiation codon was near the middle of this protected region. We have found two ribosome-binding sites in RNA 3. The principal one, near the 5′end, is the initiation site for the major translation product, a 35,000 dalton protein. The second site binds ribosomes only weakly, at the beginning of the “silent” coat protein cistron, and is similar but not identical to the initiation site protected in RNA 4. The possibility of a ribosome-binding at the “silent” cistron initiation site is discussed.