Infection of mammalian cells with picornaviruses like entero-, rhino-, and aphthoviruses leads to an inhibition of cap-dependent cellular protein synthesis by the cleavage of both translation initiation factors, eIF4GI and eIF4GII. In entero- and rhinovirus infection this cleavage process is mediated by the viral 2A proteinase (2Apro). In order to discriminate between a direct mode of eIF4G cleavage and an indirect cleavage via activation of a cellular proteinase, a thermosensitive 2Apro mutant (ts-2Apro) of human rhinovirus 2 was employed. Temperature shift experiments of cytoplasmic HeLa cell extracts incubated with ts-2Apro strongly support a direct mode of cleavage of eIF4GI and eIF4GII by the viral 2Apro.
