title: Mrd1p is required for release of base-paired U3 snoRNA within the preribosomal complex.
abstract: In eukaryotes, ribosomes are made from precursor rRNA (pre-rRNA) and ribosomal proteins in a maturation process that requires a large number of snoRNPs and processing factors. A fundamental problem is how the coordinated and productive folding of the pre-rRNA and assembly of successive pre-rRNA-protein complexes is achieved cotranscriptionally. The conserved protein Mrd1p, which contains five RNA binding domains (RBDs), is essential for processing events leading to small ribosomal subunit synthesis. We show that full function of Mrd1p requires all five RBDs and that the RBDs are functionally distinct and needed during different steps in processing. Mrd1p mutations trap U3 snoRNA in pre-rRNP complexes both in base-paired and non-base-paired interactions. A single essential RBD, RBD5, is involved in both types of interactions, but its conserved RNP1 motif is not needed for releasing the base-paired interactions. RBD5 is also required for the late pre-rRNP compaction preceding A(2) cleavage. Our results suggest that Mrd1p modulates successive conformational rearrangements within the pre-rRNP that influence snoRNA-pre-rRNA contacts and couple U3 snoRNA-pre-rRNA remodeling and late steps in pre-rRNP compaction that are essential for cleavage at A(0) to A(2). Mrd1p therefore coordinates key events in biosynthesis of small ribosome subunits.
authors.affiliation: Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden.
authors.forename: Pär
authors.initials: P
authors.lastname: Lundkvist
authors.forename: Sara
authors.initials: S
authors.lastname: Jupiter
authors.forename: Asa
authors.initials: A
authors.lastname: Segerstolpe
authors.forename: Yvonne N
authors.initials: YN
authors.lastname: Osheim
authors.forename: Ann L
authors.initials: AL
authors.lastname: Beyer
authors.forename: Lars
authors.initials: L
authors.lastname: Wieslander
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D020029:Base Pairing / Q000235:genetics*; D005472:Fluorouracil / Q000494:pharmacology; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005799:Genes, Dominant; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009963:Orotic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D020537:RNA, Small Nucleolar / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C530595:Mrd1 protein, S cerevisiae; D050505:Mutant Proteins; D012322:RNA Precursors; D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins; D009963:Orotic Acid; C001242:5-fluoroorotic acid; D005472:Fluorouracil
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