ALTERNATIVELY SPLICED TRANSCRIPTS FROM THE DROSOPHILA-EIF4E GENE PRODUCE 2 DIFFERENT CAP-BINDING PROTEINS

Eukaryotic initiation factor 4E (eIF4E) is the subunit of eIF4F that b inds to the cap structure at the 5' end of messenger RNA and is a crit ical component for the regulation of translation initiation. Using 7-m ethyl-GTP-Sepharose affinity chromatography, two distinct cap-binding proteins that migrate on SDS-polyacrylamide gel electrophoresis at app roximately 35 kDa were purified from Drosophila adults. Peptide micros equence analysis indicated that these two proteins differ at their ami no termini. Analysis of a set of cDNA clones encoding eIF4E led to the conclusion that the two different protein isoforms, which we term eIF 4EI and eIF4EII, result from three alternatively spliced transcripts f rom a single eIF4E gene, which maps to region 67A8-B2 on polytene chro mosomes. The three eIF4E transcripts also vary greatly in the lengths of their 5'-UTRs, suggesting the possibility of complex translational control of expression of the two eIF4E isoforms.