Analysis of two human pre-ribosomal factors, bystin and hTsr1, highlights differences in evolution of ribosome biogenesis between yeast and mammals

Nucleic Acids Res. 2011 Jan;39(1):280-91. doi: 10.1093/nar/gkq734. Epub 2010 Aug 30.


Recent studies reveal that maturation of the 40S ribosomal subunit precursors in mammals includes an additional step during processing of the internal transcribed spacer 1 (ITS1), when compared with yeast Saccharomyces cerevisiae, even though the protein content of the pre-40S particle appears to be the same. Here, we examine by depletion with siRNA treatment the function of human orthologs of two essential yeast pre-ribosomal factors, hEnp1/bystin and hTsr1. Like their yeast orthologs, bystin is required for efficient cleavage of the ITS1 and further processing of this domain within the pre-40S particles, whereas hTsr1 is necessary for the final maturation steps. However, bystin depletion leads to accumulation of an unusual 18S rRNA precursor, revealing a new step in ITS1 processing that potentially involves an exonuclease. In addition, pre-40S particles lacking hTsr1 are partially retained in the nucleus, whereas depletion of Tsr1p in yeast results in strong cytoplasmic accumulation of pre-40S particles. These data indicate that ITS1 processing in human cells may be more complex than currently envisioned and that coordination between maturation and nuclear export of pre-40S particles has evolved differently in yeast and mammalian cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus
  • Biological Evolution
  • Cell Adhesion Molecules / antagonists & inhibitors
  • Cell Adhesion Molecules / chemistry
  • Cell Adhesion Molecules / physiology*
  • Cell Nucleus / metabolism
  • Gene Knockdown Techniques
  • HeLa Cells
  • Humans
  • Nuclear Proteins / chemistry
  • RNA Precursors / metabolism
  • RNA Processing, Post-Transcriptional*
  • RNA, Ribosomal / metabolism*
  • Ribosomal Proteins / antagonists & inhibitors
  • Ribosomal Proteins / chemistry
  • Ribosomal Proteins / physiology*
  • Ribosome Subunits, Small, Eukaryotic / metabolism*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Sequence Homology, Amino Acid


  • BYSL protein, human
  • Cell Adhesion Molecules
  • ENP1 protein, S cerevisiae
  • Nuclear Proteins
  • RNA Precursors
  • RNA, Ribosomal
  • Ribosomal Proteins
  • Saccharomyces cerevisiae Proteins
  • Tsr1 protein, human