Cloning of cDNA for the γ-subunit of mammalian translation initiation factor 2B, the guanine nucleotide-exchange factor for eukaryotic initiation factor 2

Peptide sequence data were obtained from rabbit protein synthesis initiation factor subunit eIF2Bγ. Searching the database of expressed sequence tags (dbEST) revealed nucleotide sequences potentially encoding human eIF2Bγ that contained peptides corresponding to those from the rabbit subunit. PCR primers were derived from these sequences and used to generate a probe. This was used to screen a rat skeletal muscle cDNA library, and a clone encoding rat eIF2Bγ was isolated. This cDNA gave a product in coupled transcription/translation that co-migrated with the γ-subunit of purified eIF2B under SDS/PAGE. The sequence of this rat eIF2Bγ cDNA is reported. The protein sequence shows homology with that of yeast eIF2Bγ (the GCD1 gene product). We have also identified an open reading frame from the Caenorhabditis elegans genome project that probably encodes the γ-subunit of C. elegans eIF2B. All these sequences show similarity to nucleotidyl- and acyltransferases, as previously reported for GCD1 [Koonin (1995) Protein Sci. 4, 1608–1617], and contain conserved motifs potentially involved in nucleotide binding. They also contain ‘I-patch’ motifs: isoleucine-rich hexamer repeats that have been associated with the binding of acyl groups in bacterial acyltransferases. The roles of these motifs are discussed in relation to the known properties of eIF2B.