Abstract
Eukaryotic initiation factor 4E (eIF4E) is the subunit of eIF4F that binds to the cap structure at the 5' end of messenger RNA and is a critical component for the regulation of translation initiation. Using 7-methyl-GTP-Sepharose affinity chromatography, two distinct cap-binding proteins that migrate on SDS-polyacrylamide gel electrophoresis at approximately 35 kDa were purified from Drosophila adults. Peptide microsequence analysis indicated that these two proteins differ at their amino termini. Analysis of a set of cDNA clones encoding eIF4E led to the conclusion that the two different protein isoforms, which we term eIF4EI and eIF4EII, result from three alternatively spliced transcripts from a single eIF4E gene, which maps to region 67A8-B2 on polytene chromosomes. 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.
Highlights
A single gene encoding eIF4E has been cloned in the following organisms: yeast, Drosophila, and three mammalian species (Altmann et al, 1987, 1989; Metz et al, 1992; Rychlik et al, 1987, 1992; Hernandez and Sierra, 1995)
Two Distinct 35-kDa Cap-binding Proteins in Drosophila Adults—Using extracts prepared from Drosophila adults, we purified cap-binding proteins by m7GTP-Sepharose column chromatography
In accordance with previous reports (Maroto and Sierra, 1989; Zapata et al, 1994; Duncan et al, 1995), the major cap binding activity migrates at approximately 35 kDa on SDS-polyacrylamide gel electrophoresis; our gels resolved two distinct polypeptide bands (Fig. 1A, lane c)
Summary
A single gene encoding eIF4E has been cloned in the following organisms: yeast, Drosophila, and three mammalian species (Altmann et al, 1987, 1989; Metz et al, 1992; Rychlik et al, 1987, 1992; Hernandez and Sierra, 1995). A 35-kDa cap-binding protein resembling eIF4E has been purified previously from Drosophila (Maroto and Sierra, 1989; Zapata et al, 1994).
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