Interaction of elF4G with poly(A)-binding protein stimulates translation and is critical for Xenopus oocyte maturation

The poly(A)-binding protein Pab1p interacts directly with the eukaryotic tr anslation initiation factor 4G (elF4G) to facilitate translation initiation of polyadenylated mRNAs in yeast [1,2]. Although the eIF4G-PABP interactio n has also been demonstrated in a mammalian system [3,4], its biological si gnificance in vertebrates is unknown. In Xenopus oocytes, cytoplasmic polya denylation of several mRNAs coincides with their translational activation a nd is critical for maturation [5-7]. Because the amount of PABP is very low in oocytes [8], it has been argued that the eIF4G-PABP interaction does no t play a major role in translational activation during oocyte maturation. A lso, overexpression of PABP in Xenopus oocytes has only a modest stimulator y effect on translation of polyadenylated mRNA and does not alter either th e efficiency or the kinetics of progesterone-induced maturation [9]. Here, we report that the expression of an eIF4GI mutant defective in PABP binding in Xenopus oocytes reduces translation of polyadenylated mRNA and dramatic ally inhibits progesterone-induced maturation. Our results show that the eI F4G-PABP interaction is critical for translational control of maternal mRNA s during Xenopus development.