Physical and genetic interactions of yeast Cwc21p, an ortholog of human SRm300/SRRM2, suggest a role at the catalytic center of the spliceosome

RNA. 2009 Dec;15(12):2161-73. doi: 10.1261/rna.1908309. Epub 2009 Oct 23.


In Saccharomyces cerevisiae, Cwc21p is a protein of unknown function that is associated with the NineTeen Complex (NTC), a group of proteins involved in activating the spliceosome to promote the pre-mRNA splicing reaction. Here, we show that Cwc21p binds directly to two key splicing factors-namely, Prp8p and Snu114p-and becomes the first NTC-related protein known to dock directly to U5 snRNP proteins. Using a combination of proteomic techniques we show that the N-terminus of Prp8p contains an intramolecular fold that is a Snu114p and Cwc21p interacting domain (SCwid). Cwc21p also binds directly to the C-terminus of Snu114p. Complementary chemical cross-linking experiments reveal reciprocal protein footprints between the interacting Prp8 and Cwc21 proteins, identifying the conserved cwf21 domain in Cwc21p as a Prp8p binding site. Genetic and functional interactions between Cwc21p and Isy1p indicate that they have related functions at or prior to the first catalytic step of splicing, and suggest that Cwc21p functions at the catalytic center of the spliceosome, possibly in response to environmental or metabolic changes. We demonstrate that SRm300, the only SR-related protein known to be at the core of human catalytic spliceosomes, is a functional ortholog of Cwc21p, also interacting directly with Prp8p and Snu114p. Thus, the function of Cwc21p is likely conserved from yeast to humans.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Biocatalysis*
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism*
  • Conserved Sequence
  • Humans
  • Molecular Sequence Data
  • Protein Binding
  • Protein Folding
  • Protein Interaction Domains and Motifs
  • RNA-Binding Proteins / chemistry
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Ribonucleoprotein, U4-U6 Small Nuclear / genetics
  • Ribonucleoprotein, U4-U6 Small Nuclear / metabolism
  • Ribonucleoprotein, U5 Small Nuclear / genetics
  • Ribonucleoprotein, U5 Small Nuclear / metabolism
  • Saccharomyces cerevisiae / chemistry
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / genetics*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Alignment
  • Spliceosomes / metabolism*


  • Carrier Proteins
  • Cwc21 protein, S cerevisiae
  • PRP8 protein, S cerevisiae
  • RNA-Binding Proteins
  • Ribonucleoprotein, U4-U6 Small Nuclear
  • Ribonucleoprotein, U5 Small Nuclear
  • SNU114 protein, S cerevisiae
  • SRRM2 protein, human
  • Saccharomyces cerevisiae Proteins