title: Position of eukaryotic translation initiation factor eIF1A on the 40S ribosomal subunit mapped by directed hydroxyl radical probing.
abstract: The universally conserved eukaryotic initiation factor (eIF), eIF1A, plays multiple roles throughout initiation: it stimulates eIF2/GTP/Met-tRNA(i)(Met) attachment to 40S ribosomal subunits, scanning, start codon selection and subunit joining. Its bacterial ortholog IF1 consists of an oligonucleotide/oligosaccharide-binding (OB) domain, whereas eIF1A additionally contains a helical subdomain, N-terminal tail (NTT) and C-terminal tail (CTT). The NTT and CTT both enhance ribosomal recruitment of eIF2/GTP/Met-tRNA(i)(Met), but have opposite effects on the stringency of start codon selection: the CTT increases, whereas the NTT decreases it. Here, we determined the position of eIF1A on the 40S subunit by directed hydroxyl radical cleavage. eIF1A's OB domain binds in the A site, similar to IF1, whereas the helical subdomain contacts the head, forming a bridge over the mRNA channel. The NTT and CTT both thread under Met-tRNA(i)(Met) reaching into the P-site. The NTT threads closer to the mRNA channel. In the proposed model, the NTT does not clash with either mRNA or Met-tRNA(i)(Met), consistent with its suggested role in promoting the 'closed' conformation of ribosomal complexes upon start codon recognition. In contrast, eIF1A-CTT appears to interfere with the P-site tRNA-head interaction in the 'closed' complex and is likely ejected from the P-site upon start codon recognition.
authors: Department of Microbiology and Immunology, SUNY Downstate Medical Center, NY, USA.
authors: Yingpu
authors: Y
authors: Yu
authors: Assen
authors: A
authors: Marintchev
authors: Victoria G
authors: VG
authors: Kolupaeva
authors: Anett
authors: A
authors: Unbehaun
authors: Tatyana
authors: T
authors: Veryasova
authors: Shao-Chiang
authors: SC
authors: Lai
authors: Peng
authors: P
authors: Hong
authors: Gerhard
authors: G
authors: Wagner
authors: Christopher U T
authors: CU
authors: Hellen
authors: Tatyana V
authors: TV
authors: Pestova
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015977:Eukaryotic Initiation Factor-1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017665:Hydroxyl Radical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D012337:RNA, Ribosomal, 18S / Q000737:chemistry; D011817:Rabbits; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry* / Q000378:metabolism
chemical_list: D015977:Eukaryotic Initiation Factor-1; D012337:RNA, Ribosomal, 18S; C026022:eukaryotic peptide initiation factor-1A; D017665:Hydroxyl Radical