| Popis: |
Serum starvation and readdition of serum, insulin, or mitogens result in changes in phosphorylation of several eukaryotic initiation factors that correlate with a decrease or stimulation in translation, respectively. We have introduced in vitro synthesized reporter mRNAs into exponentially growing and serum-deprived 3T3-L1 cells to examine whether serum deprivation affects cap-dependent translation. In serum-fed control cells, addition of a cap to poly(A)- or poly(A)+ mRNA increased translational efficiency by 43- and 460-fold, respectively. In serum-deprived cells, the relative rate of translational efficiency of capped mRNA was reduced 2.6-fold relative from that observed in serum-fed cells with little change in the relative functional half-life. The effect of serum deprivation on translation was rapid and occurred within 90 min, and cap function was restored upon addition of serum or insulin to starved cells. Analysis of the dose dependence for reversal of the effects of serum starvation on cap-dependent translation indicated that 10 nM insulin was optimal. Little change in the function of the poly(A) tail was observed during serum starvation or hormone treatment. However, a decrease in the synergism between the cap and a poly(A) tail was observed upon starvation which was reversed by serum, and in part, by insulin. |
