Cloning and characterization of human eIF4E genes

Two human eukaryotic initiation factor 4E (eIF4E) genes were isolated and characterized from placental and chromosome 4-specific genomic libraries. One of the genes (EIF4E1) contained six introns, but the other gene (EIF4E2) was intronless, flanked by Alu sequences and 14-base pair (bp) direct repeats, and terminated by a short poly(A) stretch, all characteristics of retrotransposons. Numerous additional intronless eIF4E pseudogenes were found, but unlike EIF4E2, all contained premature in-frame stop codons. The entire EIF4E1 gene spanned >50 kilobase pairs. The coding regions of these two genes differed in four nucleotide residues, resulting in two amino acid differences in the predicted proteins. The promoter of EIF4E1 has been characterized previously. The putative promoter of EIF4E2 contained no TATA box but did contain a transcription initiator region (Inr) and numerous other sequence motifs characteristic of regulated promoters. EIF4E2 contained only two of the three polyadenylation signals present in EIF4E1. Evidence for transcription of both genes was obtained from primer extension, S1 mapping, ribonuclease protection, and reverse transcriptase-polymerase chain reaction experiments. Transcription was found to initiate 19 bp upstream of the translational initiation codon in the case of EIF4E1 and 80 bp in the case of EIF4E2. The two genes were differentially expressed in four human cell lines, Wish, Chang, K562, and HeLa.