Translation initiation on foot-and-mouth disease
virus (FMDV) RNA occurs by a cap-independent mechanism
directed by a highly structured element (∼435 nt) termed
an internal ribosome entry site (IRES). A functional assay
to identify proteins that bind to the FMDV IRES and are
necessary for FMDV IRES-mediated translation initiation
has been developed. In vitro-transcribed polyadenylated
RNAs corresponding to the whole or part of the FMDV IRES
were immobilized on oligo-dT Dynabeads and used to deplete
rabbit reticulocyte lysate (RRL) of IRES-binding proteins.
Translation initiation factors eIF4G, eIF4A, and eIF4B
bound to the 3′ domain of the FMDV IRES. Depletion
of eIF4G from RRL by this region of the FMDV IRES correlated
with the loss of translational capacity of the RRL for
capped, uncapped, and FMDV IRES-dependent mRNAs. However,
this depleted RRL still supported hepatitis C virus IRES-directed
translation. Poly (rC) binding protein-2 bound to the central
domain of the FMDV IRES, but depletion of RRL with this
IRES domain had no effect on FMDV IRES-directed translation
initiation.