The Aphtho- and Cardiovirus “Primary” 2A/2B Polyprotein “Cleavage”

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Abstract
In the case of the aphtho- and cardioviruses, the primary cleavage in the region of the polyprotein was known to be different, occurring at the C terminus of 2A. Precursor forms spanning the 2A/2B junction are not observed in aphtho- or cardiovirus polyprotein processing. Deletions downstream of 2A did not appear to affect cleavage. Experiments analyzing the endogenous processing properties of recombinant aphthovirus indicated that the cleavage activity could be a property of the 2A oligopeptidic region alone. Consistent with this notion, studies on the endogenous processing properties of domains of the cardiovirus Theiler’s murine encephalomyelitis virus (TMEV) polyprotein localized the 2A/2B cleavage activity within the 2AB region. With artificial reporter polyprotein systems the 2A/2B cleavage activity of both EMCV and TMEV was subsequently mapped to the C-terminal 18 aa of their 2A proteins—these cardiovirus sequences being as efficient as the FMDV 2A in mediating cleavage. The molar excess of the translation product N terminal of 2A over that C-terminal of 2A is a product of inserting the 2A sequence into our artificial polyprotein systems. In summary, the authors and others have shown the aphtho- and cardiovirus 2A/2B cleavage is mediated by an oligopeptidic region, representing either the whole (aphthoviruses) or part (cardioviruses) of the 2A region.