title: Dual function of eIF3j/Hcr1p in processing 20 S pre-rRNA and translation initiation.
abstract: eIF3j/Hcr1p, a protein associated with eIF3, was shown to bind to, and stabilize, the multifactor complex containing eIFs 1, 2, 3, and 5 and Met-tRNA(i)(Met), whose formation is required for an optimal rate of translation initiation. Here we present evidence that eIF3j/Hcr1p is an RNA binding protein that enhances a late step in 40 S ribosome maturation involving cleavage of the 20 S precursor of 18 S rRNA in the cytoplasm. Immunofluorescence staining shows that eIF3j/Hcr1p is localized predominantly in the cytoplasm. The hcr1Delta mutant exhibits a decreased amount of 40 S subunits, hypersensitivity to paromomycin, and increased levels of 20 S pre-rRNA. Combining the hcr1Delta mutation with drs2Delta or rps0aDelta, deletions of two other genes involved in the same step of 40 S subunit biogenesis, produced a synthetic growth defect. p35, the human ortholog of eIF3j/Hcr1p, partially complemented the slow growth phenotype conferred by hcr1Delta when overexpressed in yeast. heIF3j/p35 was found physically associated with yeast eIF3 and 43 S initiation complexes in vitro and in vivo. Because it did not complement the 40 S biogenesis defect of hcr1Delta, it appears that heIF3j can substitute for eIF3j/Hcr1p only in translation initiation. We conclude that eIF3j/Hcr1p is required for rapid processing of 20 S to 18 S rRNA besides its role in translation initiation, providing an intriguing link between ribosome biogenesis and translation.
authors.affiliation: Laboratory of Gene Regulation and Development, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: L
authors.initials: L
authors.lastname: Valásek
authors.forename: J
authors.initials: J
authors.lastname: Hasek
authors.forename: K H
authors.initials: KH
authors.lastname: Nielsen
authors.forename: A G
authors.initials: AG
authors.lastname: Hinnebusch
mesh_terms: D000483:Alleles; D015153:Blotting, Western; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D039621:Eukaryotic Initiation Factor-3; D019084:Fluorescent Antibody Technique, Indirect; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D006801:Humans; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D010303:Paromomycin / Q000737:chemistry; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D012322:RNA Precursors / Q000737:chemistry*; D012335:RNA, Ribosomal / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S; D012270:Ribosomes / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D039621:Eukaryotic Initiation Factor-3; D005656:Fungal Proteins; C121939:HCR1 protein, S cerevisiae; D010448:Peptide Initiation Factors; D012322:RNA Precursors; D012335:RNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D029701:Saccharomyces cerevisiae Proteins; D010303:Paromomycin