Translational repression of EF‐1α mRNA in vitro

In this report we show that when 10000 ×g supernatant extracts of growth arrested murine erythroleukemia (MEL) cells are incubated there is a rapid conversion of essentially all mRNAs to non‐translating messenger ribonucleoprotein (RNP) particles. Most of these RNPs are readily translated in an initiation‐dependent manner when added to a nuclease‐treated rabbit reticulocyte lysate. A notable exception is the RNP containing eucaryotic elongation factor 1α (EF‐1α) mRNA. The mRNA for poly(A)‐binding protein behaved similarly to EF‐1α. Previous work has demonstrated that the translation of both these mRNAs are repressed in vivo when the growth of a number of different mammalian cells is arrested [Slobin L. I. and Jordan, P. (1984) Eur J. Biochem. 145, 1984; Thomas, G. and Thomas, G. (1986) J. Cell Biol. 103, 1986]. Translational activity of EF‐1α mRNA could be restored by treating RNP particles with 0.5 M KCl, provided that the RNPs were separated from salt wash by chromatography on oligo(dT)‐cellulose. Addition of the salt wash to total MEL cell mRNA significantly and selectively inhibited EF‐ 1α mRNA translation, suggesting that a component of the salt wash acts as a trans‐acting translational repressor of EF‐1α mRNA.