title: Multiple RNA interactions position Mrd1 at the site of the small subunit pseudoknot within the 90S pre-ribosome.
abstract: Ribosomal subunit biogenesis in eukaryotes is a complex multistep process. Mrd1 is an essential and conserved small (40S) ribosomal subunit synthesis factor that is required for early cleavages in the 35S pre-ribosomal RNA (rRNA). Yeast Mrd1 contains five RNA-binding domains (RBDs), all of which are necessary for optimal function of the protein. Proteomic data showed that Mrd1 is part of the early pre-ribosomal complexes, and deletion of individual RBDs perturbs the pre-ribosomal structure. In vivo ultraviolet cross-linking showed that Mrd1 binds to the pre-rRNA at two sites within the 18S region, in helix 27 (h27) and helix 28. The major binding site lies in h27, and mutational analyses shows that this interaction requires the RBD1-3 region of Mrd1. RBD2 plays the dominant role in h27 binding, but other RBDs also contribute directly. h27 and helix 28 are located close to the sequences that form the central pseudoknot, a key structural feature of the mature 40S subunit. We speculate that the modular structure of Mrd1 coordinates pseudoknot formation with pre-rRNA processing and subunit assembly.
authors.affiliation: Department of Molecular Biology and Functional Genomics, Stockholm University SE-106 91, Stockholm, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Segerstolpe
authors.forename: Sander
authors.initials: S
authors.lastname: Granneman
authors.forename: Petra
authors.initials: P
authors.lastname: Björk
authors.forename: Flavia
authors.initials: F
authors.lastname: de Lima Alves
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.forename: Charlotta
authors.initials: C
authors.lastname: Andersson
authors.forename: Martin
authors.initials: M
authors.lastname: Högbom
authors.forename: David
authors.initials: D
authors.lastname: Tollervey
authors.forename: Lars
authors.initials: L
authors.lastname: Wieslander
mesh_terms: D001665:Binding Sites; D009690:Nucleic Acid Conformation; D017434:Protein Structure, Tertiary; D012322:RNA Precursors / Q000737:chemistry / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion
chemical_list: C530595:Mrd1 protein, S cerevisiae; D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins