title: Structural Heterogeneity in Pre-40S Ribosomes.
abstract: Late-stage 40S ribosome assembly is a highly regulated dynamic process that occurs in the cytoplasm, alongside the full translation machinery. Seven assembly factors (AFs) regulate and facilitate maturation, but the mechanisms through which they work remain undetermined. Here, we present a series of structures of the immature small subunit (pre-40S) determined by three-dimensional (3D) cryoelectron microscopy with 3D sorting to assess the molecule's heterogeneity. These structures demonstrate an extensive structural heterogeneity of interface AFs that likely regulates subunit joining during 40S maturation. We also present structural models for the beak and the platform, two regions where the low resolution of previous studies did not allow for localization of AFs and the rRNA, respectively. These models are supported by biochemical analyses using point variants and suggest that maturation of the 18S 3' end is regulated by dissociation of the AF Dim1 from the subunit interface, consistent with previous biochemical analyses.
authors.affiliation: Department of Biological Science, Institute of Molecular Biophysics, Florida State University, 91 Chieftain Way, Tallahassee, FL 32306, USA.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Johnson
authors.affiliation: Department of Cancer Biology, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Homa
authors.initials: H
authors.lastname: Ghalei
authors.affiliation: Department of Cancer Biology, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Katelyn A
authors.initials: KA
authors.lastname: Doxtader
authors.affiliation: Department of Cancer Biology, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Katrin
authors.initials: K
authors.lastname: Karbstein
authors.affiliation: Department of Biological Science, Institute of Molecular Biophysics, Florida State University, 91 Chieftain Way, Tallahassee, FL 32306, USA. Electronic address: mestroupe@bio.fsu.edu.
authors.forename: M Elizabeth
authors.initials: ME
authors.lastname: Stroupe
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D003001:Cloning, Molecular; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D018740:Genetic Heterogeneity; D006801:Humans; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D012335:RNA, Ribosomal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017415:Ribonucleoprotein, U5 Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism / Q000648:ultrastructure*; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000648:ultrastructure*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: C405962:NOB1 protein, S cerevisiae; D009687:Nuclear Proteins; C474861:PNO1 protein, S cerevisiae; D012335:RNA, Ribosomal; C578290:RPS3 protein, human; D011994:Recombinant Proteins; D017415:Ribonucleoprotein, U5 Small Nuclear; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C506012:TXNL4A protein, human; C555735:Tsr1 protein, human
keywords: cryo-EM; pre-40S ribosome; ribosome assembly; ribosome biogenesis; small subunit assembly