Translation initiation factor IF2 of the myxobacterium Stigmatella aurantiaca: presence of a single species with an unusual N-terminal sequence

Abstract

The structural gene for translation initiation factor IF2 (infB) was isolated from the myxobacterium Stigmatella aurantiaca on a 5.18-kb BamHI 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 coli, Bacillus subtilis, Bacillus stearothermophilus, and Streptococcus faecium. The N-terminal region does not display any significant homology to other known proteins. The S. aurantiaca infB gene encodes a single 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 distinguished from all other IF2s by a sequence of 160 residues near the N terminus that has an unusual composition, made up essentially of alanine, proline, valine, and glutamic acid. Within this sequence, the pattern PXXXAP is repeated nine times. Complete deletion of this sequence did not affect the factor's function in initiation of translation and even increased its capacity to complement the E. coli infB mutant.Myxobacteria are gram-negative, rod-shaped soil bacteria which, in response to starvation, undergo a developmental cycle leading to multicellular structures termed fruiting bodies. These specialized structures enclose dormant cells, the myxospores (41). Multicellular development of myxobacteria is regulated by intercellular signals, with some of them presumably transduced by GTP-binding proteins as in eukaryotes (8,25), and by cell-cell interactions (10). The expression of specific sets of genes is coordinated via various signalling compounds, thus triggering the different stages of multicellular development (24). For another sporulating bacterium, Bacillus subtilis, Tipper et al. (45) suggested that some components of the translational machinery, namely ribosomal proteins and elongation factor G, could play a specific role during the spore formation process. In agreement with this idea, Cheng et al. (6) identified the lesions in a Myxococcus xanthus development-deficient strain displaying a mutation in dsg, encoding a protein similar to translation initiation factor IF3. Compared to IF3s from other species, the Myxococcus IF3 is much larger and bears a C-terminal extension which was shown to be necessary for developmental functions but not for viability, even though during vegetative growth, colonies were shown to be more compact and to be a darker tan color (19).In addition to IF3, at least two other factors, IF1 and IF2, are required for the initiation of mRNA translation in prokaryotes. The genes for all three factors, namely, infA (IF1), infB (IF2), and infC (IF3), were first cloned in Escherichia coli (30,36,43). These three proteins play essential roles in several steps of translation initiation, from the selection of the initiator tRNA (15) to the control of the entry into the elongation cycle (26).The infB gene, encoding IF2, is located on the E. coli chromosome at 69 min and is part of a complex polycis...

Modulation of ribosomal recruitment to 5′‐terminal start codons by translation initiation factors IF2 and IF3

“…Plasmid pLBYC8 is a derivative of the high copy number plasmid pTrc99A (Pharmacia Biotech.) and encodes the E. coli infB gene [14].…”

“…translational autoregulation by IF3 [25,26], with plasmid pLBYC8 harboring the E. coli infB gene [14], with both plasmids pKAUGinfC and pLBYC8, or with both the parental control plasmids pK184 and pTrc99A. The L-galactosidase activity obtained with the control strain MC4100FPVWH103(pK184; pTrc99A) was set to 1.…”

Initiation of Protein Synthesis in Bacteria

“…stearothermophilus and T. thermophilus IF2 possess a single domain in the region N-terminal to the G-domain, whereas myxobacterial IF2, which has the longest N-terminal regions characterized in bacteria, is composed of several domains with a highly unusual amino acid composition. The latter is a general feature of the N-terminal regions of IF2 (16,64,225,230). Regions N-terminal to the G-domain of eukaryotic IF2 homologues are generally long, up to ϳ700 amino acids, whereas the regions of the archaeal IF2 homologues are generally short.…”

Initiation Factor 2 of Myxococcus xanthus , a Large Version of Prokaryotic Translation Initiation Factor 2

“…The expression of ␣ and ␤ forms of IF2 has also been observed in Bacillus subtilis (31). On the other hand, only one form seems to exist in other bacteria such as Bacillus stearothermophilus, Streptococcus faecium, and the myxobacterium Stigmatella aurantiaca (3,4,11). There is thus no obvious pattern to the occurrence of multiple forms of IF2 in gram-negative and gram-positive bacteria or even in closely related bacilli.…”