JBC, Vol. 253, Issue 17, 5939-5945, Sep, 1978
Initiation factor eIF-4B (IF-M3)-dependent recognition and translation of capped versus uncapped eukaryotic mRNAs
M. Padilla, D. Canaani, Y. Groner, J. A. Weinstein, M. Bar-Joseph, W. Merrick and D. A. Shafritz
Translation of capped and uncapped eukaryotic mRNAs is stimulated by
addition of eIF-4B to an mRNA-dependent reticulocyte lysate system. m7G5
ppp inhibits translation of capped but not uncapped mRNAs and reduces
translation of capped vaccinia mRNA to the level obtained with uncapped
vaccinia mRNA. Exogenous eIF-4B but no other initiation factor reverses
inhibition of protein synthesis by m7G5'ppp. Both capped and uncapped mRNAs
interact directly with eIF-4B to form a stable complex, which can be
detected by a simple nitrocellulose filter binding assay. However, addition
of a 5'-cap to beta-eliminated globin mRNA or satellite tobacco necrosis
virus RNA (normally uncapped) increased binding affinity of these mRNAs for
eIF-4B and causes binding of these mRNAs to become sensitive to inhibition
by m7G5'ppp. These results indicate that the role of the mRNA 5'-cap in
translation is related specifically to the function of eIF-4B in forming a
complex with mRNA (prior to association of mRNA with the 40 S ribosomal
subunit) and that both cap and non-cap sequences participate in this
process.