The eukaryotic mRNA 3′ poly(A) tail and the 5′
cap cooperate to synergistically enhance translation. This
interaction is mediated, at least in part, by eIF4G, which bridges
the mRNA termini by simultaneous binding the poly(A)-binding
protein (PABP) and the cap-binding protein, eIF4E. The poly(A)
tail also stimulates translation from the internal ribosome
binding sites (IRES) of a number of picornaviruses. eIF4G is
likely to mediate this translational stimulation through its
direct interaction with the IRES. Here, we support this hypothesis
by cleaving eIF4G to separate the PABP-binding site from the
portion that promotes internal initiation. eIF4G cleavage abrogates
the stimulatory effect of poly(A) tail on translation. In addition,
translation in extracts in which eIF4G is cleaved is resistant
to inhibition by the PABP-binding protein 2 (Paip2). The eIF4G
cleavage-induced loss of the stimulatory effect of poly(A) on
translation was mimicked by the addition of the C-terminal portion
of eIF4G. Thus, PABP stimulates picornavirus translation through
its interaction with eIF4G.