A model for nonstoichiometric, cotranslational protein scission in eukaryotic ribosomes

The aphthovirus 2A region apparently responsible for the hydrolytic cleavage of a single large polyprotein at a Gly-Pro linkage is only 18 amino acid residues long and is evidently not a proteinase. Here we describe the construction of reporter recombinant polyproteins and provide the results of further mutagenesis experiments designed to test the functions of specific amino acid residues within the foot-and-mouth disease virus (FMDV) 2A region. These results show that a Gly-Pro amide bond is not actually synthesized. The result can be rationalized into a kinetic and structural model for cotranslational aphtho- and cardiovirus polyprotein cleavage in which hydrolysis is mediated by a ribosomally bound 2A polypeptidyl-tRNA molecule at its own 3'-O acyl adenosyl ester linkage. The possible role of the 3-D structure of the 2A polypeptide in preventing peptide bond formation but in allowing the synthesis of the downstream polypeptide sequence is discussed within the context of the new findings. (C) 1999 Academic Press.