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

Nucleic Acids Res. 2008 Aug;36(13):4364-80. doi: 10.1093/nar/gkn384. Epub 2008 Jun 27.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Nucleolus / metabolism
  • Cell Nucleus / metabolism
  • Mutation
  • Phosphoproteins / metabolism
  • RNA Precursors / metabolism*
  • RNA Processing, Post-Transcriptional
  • RNA, Ribosomal / metabolism*
  • RNA, Small Nucleolar / metabolism
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • Ribonucleoproteins / metabolism
  • Ribosomal Proteins
  • Ribosome Subunits, Small, Eukaryotic / chemistry
  • Ribosome Subunits, Small, Eukaryotic / metabolism*
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Transcription, Genetic

Substances

  • MPP10 protein, S cerevisiae
  • Mrd1 protein, S cerevisiae
  • PWP2 protein, S cerevisiae
  • Phosphoproteins
  • RNA Precursors
  • RNA, Ribosomal
  • RNA, Small Nucleolar
  • RNA, U3 small nucleolar
  • RNA-Binding Proteins
  • Recombinant Fusion Proteins
  • Ribonucleoproteins
  • Ribosomal Proteins
  • Saccharomyces cerevisiae Proteins