Cloning and characterization of complementary and genomic DNAs encoding the ε-subunit of rat translation initiation factor-2B

Eukaryotic initiation factor-2B (eIF-2B) is a guanine nucleotide-exchange protein involved in the recycling of eIF-2 during peptide-chain initiation. Regulation of eIF 2B activity occurs under a wide range of conditions by diverse mechanisms. To better understand the regulation of eIF-2B activity as well as the coordinate expression of its five subunits, we have begun to clone and characterize the cDNAs and genes encoding these proteins. In the present study, complementary and genomic DNAs encoding the ε-subunit of rat eIF-2B were cloned and characterized. The cDNA is 2517 bp in length, including a 30 nt poly(A) tail, and recognizes both 2.7 and 3.5 kb mRNA species on Northern blots of rat RNA. The cDNA contains a 2151 bp open reading frame encoding 716 amino acids producing a protein with a predicted molecular mass of 80 kDa. The derived amino acid sequence contains regions identical to three peptides obtained from bovine liver eIF-2Bε and is 31% identical to Gcd6, the putative yeast eIF-2Bε. Examination of the derived amino acid sequence of rat eIF-2Bε reveals phosphorylation site motifs for several protein kinases which have been implicated in regulation of guanine nucleotide exchange activity. The mRNA fore eIF-2Bε is expressed to a similar extent in most rat tissues examined with the exception of testis, where its expression is approx. three-fold greater. We have also isolated and sequenced the coding and 5'-flanking region of the rat eIF-2Bε gene. The 16 exons encoding rat eIF-2Bε are contained within 9.5 kb of genomic DNA. Examination of the promoter region of the gene reveals a consensus binding site for the α-Pal transcription factor as well as possible cytokine-response elements and binding sites for testis-specific transcription factors.