title: Mrd1p binds to pre-rRNA early during transcription independent of U3 snoRNA and is required for compaction of the pre-rRNA into small subunit processomes.
abstract: In Saccharomyces cerevisiae, synthesis of the small ribosomal subunit requires assembly of the 35S pre-rRNA into a 90S preribosomal complex. SnoRNAs, including U3 snoRNA, and many trans-acting proteins are required for the ordered assembly and function of the 90S preribosomal complex. Here, we show that the conserved protein Mrd1p binds to the pre-rRNA early during transcription and is required for compaction of the pre-18S rRNA into SSU processome particles. We have exploited the fact that an Mrd1p-GFP fusion protein is incorporated into the 90S preribosomal complex, where it acts as a partial loss-of-function mutation. When associated with the pre-rRNA, Mrd1p-GFP functionally interacts with the essential Pwp2, Mpp10 and U3 snoRNP subcomplexes that are functionally interconnected in the 90S preribosomal complex. The fusion protein can partially support 90S preribosome-mediated cleavages at the A(0)-A(2) sites. At the same time, on a substantial fraction of transcripts, the composition and/or structure of the 90S preribosomal complex is perturbed by the fusion protein in such a way that cleavage of the 35S pre-rRNA is either blocked or shifted to aberrant sites. These results show that Mrd1p is required for establishing productive structures within the 90S preribosomal complex.
authors.affiliation: Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91, Stockholm, Sweden.
authors.forename: Asa
authors.initials: A
authors.lastname: Segerstolpe
authors.forename: Pär
authors.initials: P
authors.lastname: Lundkvist
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: D002466:Cell Nucleolus / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism*; D020537:RNA, Small Nucleolar / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D012269:Ribosomal Proteins; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: C111098:MPP10 protein, S cerevisiae; C530595:Mrd1 protein, S cerevisiae; C100850:PWP2 protein, S cerevisiae; D010750:Phosphoproteins; D012322:RNA Precursors; D012335:RNA, Ribosomal; D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins