CLONING OF CDNA FOR THE GAMMA-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 init iation factor subunit eIF2B gamma. Searching the database of expressed sequence tags (dbEST) revealed nucleotide sequences potentially encod ing human eIF2B gamma that contained peptides corresponding to those f rom the rabbit subunit. PCR primers were derived from these sequences and used to generate a probe. This was used to screen a rat skeletal m uscle cDNA library, and a clone encoding rat eIF2B gamma was isolated. This cDNA gave a product in coupled transcription/translation that co -migrated with the gamma-subunit of purified eIF2B under SDS/PAGE. The sequence of this rat eIF2B gamma cDNA is reported. The protein sequen ce shows homology with that of yeast eIF2B gamma (the GCD1 gene produc t). We have also identified an open reading frame from the Caenorhabdi tis elegans genome project that probably encodes the gamma-subunit of C. elegans eIF2B. All these sequences show similarity to nucleotidyl- and acyltransferases, as previously reported for GCD1 [Koonin (1995) P rotein Sci. 4, 1608-1617], and contain conserved motifs potentially in volved in nucleotide binding. They also contain 'I-patch' motifs: isol eucine-rich hexamer repeats that have been associated with the binding of acyl groups in bacterial acyltransferases. The roles of these moti fs are discussed in relation to the known properties of eIF2B.