Initiation factor 2 of Myxococcus xanthus, a large version of prokaryotic translation initiation factor 2

We have isolated the structural gene for translation initiation factor IF2 (infB) from the myxobacterium Myxococcus xanthus. The gene (3.22 kb) encode s a 1,070-residue protein showing extensive homology within its G domain an d C terminus to the equivalent regions of IF2 from Escherichia coli. The pr otein cross-reacts with antibodies raised against E. coli IF2 and was able to complement an E. coli infB mutant. The M. xanthus protein is the largest IF2 known to date. This is essentially due to a longer N-terminal region m ade up of two characteristic domains. The first comprises a 188-amino-acid sequence consisting essentially of alanine, proline, valine, and glutamic a cid residues, similar to the APE domain observed in Stigmatella aurantiaca IF2. The second is unique to M. xanthus IF2, is located between the APE seq uence and the GTP binding domain, and consists exclusively of glycine, prol ine, and arginine residues.