TRANSLATION INITIATION-FACTOR IF2 OF THE MYXOBACTERIUM STIGMATELLA-AURANTIACA - PRESENCE OF A SINGLE-SPECIES WITH AN UNUSUAL N-TERMINAL SEQUENCE

The structural gene for translation initiation factor IF2 (infB) was i solated from the myxobacterium Stigmatella aurantiaca on a 5.18-kb Bam HI genomic restriction fragment. The infB gene (ca. 3.16 kb) encodes a 1,054-residue polypeptide with extensive homology within its G domain and C terminus with the equivalent regions of IF2s from Escherichia c oli, Bacillus subtilis, Bacillus stearothermophilus, and Streptococcus faecium. The N-terminal region does not display any significant homol ogy to other known proteins. The S. aurantiaca infB gene encodes a sin gle protein which cross-reacted with antiserum to E. coli IF2 and was able to complement an E. coli infB mutant. The S. aurantiaca IF2 is di stinguished from all other IF2s by a sequence of 160 residues near the N terminus that has an unusual composition, made up essentially of al anine, proline, valine, and glutamic acid. Within this sequence, the p attern PXXXAP is repeated nine times. Complete deletion of this sequen ce did not affect the factor's function in initiation of translation a nd even increased its capacity to complement the E. coli infB mutant.