The structure of the translational initiation factor IF1 from E.coli contains an oligomer-binding motif

Abstract

Initiation factor IF1, the smallest of the three factors, (Cummings and Hershey, 1994), indicating that one or more of the activities of IF1 must The structure of the translational initiation factor be essential for the cell. Maurizio IF1 from Escherichia coli has been determined withSeveral functions have been reported for IF1. These multidimensional NMR spectroscopy. Using 1041 disinclude: (i) the enhancement of the rate of 70S ribosome tance and 78 dihedral constraints, 40 distance geometry dissociation and subunit association (Godefroy-Colburn structures were calculated, which were refined by et al., 1975); (ii) the stimulation of the activity of IF2 restrained molecular dynamics. From this set, 19 strucand IF3 in the formation of the 30S initiation complex tures were selected, having low constraint energy and (Wintermeyer and Gualerzi, 1983; Pon and Gualerzi, few constraint violations. The ensemble of 19 structures 1984); and (iii) the modulation of the interaction of IF2 displays a root-mean-square deviation versus the averwith the ribosome, increasing its affinity for the 30S age of 0.49 Å for the backbone atoms and 1.12 Å for ribosomal subunit when IF1 is bound and indirectly all atoms for residues 6-36 and 46-67. The structure favouring its release when IF1 is ejected (Stringer et al., of IF1 is characterized by a five-stranded β-barrel.1977; Celano et al., 1988). In addition, by binding to the The loop connecting strands three and four contains a A-site of the 30S ribosomal subunit, IF1 may contribute short 3 10 helix but this region shows considerably to the fidelity of the selection of the initiation site of the higher flexibility than the β-barrel. The fold of IF1 is mRNA (Moazed et al., 1995). very similar to that found in the bacterial cold shock Equilibrium binding studies have shown that IF1 binds proteins CspA and CspB, the N-terminal domain of to the 30S ribosomal subunit in a 1:1 ratio (Zucker and aspartyl-tRNA synthetase and the staphylococcal Hershey, 1986;Celano et al., 1988). The binding affinity nuclease, and can be identified as the oligomer-binding depends strongly upon the ionic strength and upon the motif. Several proteins of this family are nucleic acidpresence of IF2 and IF3 which increase its affinity for the binding proteins. This suggests that IF1 plays its role ribosome; the K a ranging from 5ϫ10 5 to 2.5ϫ10 8 M -1 . in the initiation of protein synthesis by nucleic acid Interaction with 50S ribosomal subunits was also observed, interactions. Specific changes of NMR signals of IF1 but the affinity is considerably lower than for the 30S upon titration with 30S ribosomal subunit identifies ribosomal subunits. Stable interaction with 70S ribosomes several residues that are involved in the interaction has never been observed; in fact, the addition of 50S to with ribosomes.

In vivo involvement of mutated initiation factor IF1 in gene expression control at the translational level

“…It is known that IF1 is an RNA binding protein being a member of the oligonucleotide/oligosaccharide binding fold (OB-fold) family of proteins [12], which among others includes RNA-binding proteins such as the cold shock protein CspA [14] and eIF1A [13,15]. IF1 displays a striking structural resemblance to the major cold shock protein CspA [34,35].…”

“…It is a member of the oligonucleotide/oligosaccharide binding (OB) fold family of proteins [12], which among others includes RNA-binding proteins such as ribosomal protein S1 [13], the cold shock protein CspA [12,14] and eukaryotic initiation factor (eIF1A) [13,15].…”

Many Parallel Losses of infA from Chloroplast DNA during Angiosperm Evolution with Multiple Independent Transfers to the Nucleus

“…In E. coli , three initiation factors (IFs) mediate the coming together of the mRNA, ribosome, and initiator tRNA-Met to begin translation. IF1 is the smallest of these factors (only 72 residues long) and consists of an RNA binding domain whose precise molecular role is unclear (Sette et al, 1997;Battiste et al, 2000). The initiation of translation in organelles is thought to be similar to that in E. coli , although much less is known about the organelle systems (Pel and Grivell, 1994;Yu and Spremulli, 1998).…”

Coupled Release of Eukaryotic Translation Initiation Factors 5B and 1A from 80S Ribosomes following Subunit Joining

“…Like bacterial IF1, eIF1A possesses a conserved ␤-barrel fold (5,34); however, the eukaryotic factor has in addition a helical element that packs against the core domain and the N-and C-terminal nonstructured tails. eIF1A functionally coordinates with eIF1 and promotes 43S complex formation, as well as ribosomal scanning and AUG start codon recognition (12,23,29).…”