The aphthovirus 2A region apparently responsible for the hydrolytic cleavag
e 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 const
ruction of reporter recombinant polyproteins and provide the results of fur
ther mutagenesis experiments designed to test the functions of specific ami
no 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. T
he result can be rationalized into a kinetic and structural model for cotra
nslational aphtho- and cardiovirus polyprotein cleavage in which hydrolysis
is mediated by a ribosomally bound 2A polypeptidyl-tRNA molecule at its ow
n 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 th
e context of the new findings. (C) 1999 Academic Press.