90S pre-ribosomes include the 35S pre-rRNA, the U3 snoRNP, and 40S subunit processing factors but predominantly lack 60S synthesis factors

Mol Cell. 2002 Jul;10(1):105-15. doi: 10.1016/s1097-2765(02)00579-8.


We report the characterization of early pre-ribosomal particles. Twelve TAP-tagged components each showed nucleolar localization, sedimented at approximately 90S on sucrose gradients, and coprecipitated both the 35S pre-rRNA and the U3 snoRNA. Thirty-five non-ribosomal proteins were coprecipitated, including proteins associated with U3 (Nop56p, Nop58p, Sof1p, Rrp9, Dhr1p, Imp3p, Imp4p, and Mpp10p) and other factors required for 18S rRNA synthesis (Nop14p, Bms1p, and Krr1p). Mutations in components of the 90S pre-ribosomes impaired 40S subunit assembly and export. Strikingly, few components of recently characterized pre-60S ribosomes were identified in the 90S pre-ribosomes. We conclude that the 40S synthesis machinery predominately associates with the 35S pre-rRNA factors, whereas factors required for 60S subunit synthesis largely bind later, showing an unexpected dichotomy in binding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Northern
  • Blotting, Western
  • Centrifugation, Density Gradient
  • Electrophoresis, Polyacrylamide Gel
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • Macromolecular Substances
  • Molecular Weight
  • Protein Subunits
  • RNA Precursors / metabolism*
  • RNA, Ribosomal / metabolism*
  • Ribonucleoproteins, Small Nucleolar / metabolism*
  • Ribosomes / chemistry*
  • Ribosomes / genetics
  • Ribosomes / metabolism*
  • Yeasts / cytology*
  • Yeasts / genetics*


  • Fungal Proteins
  • Macromolecular Substances
  • Protein Subunits
  • RNA Precursors
  • RNA, Ribosomal
  • Ribonucleoproteins, Small Nucleolar
  • ribonucleoprotein, U3 small nucleolar