Structural basis of the interaction between P-element somatic inhibitor and U1-70k essential for the alternative splicing of P-element transposase

J Mol Biol. 2005 Aug 5;351(1):52-65. doi: 10.1016/j.jmb.2005.04.077.


P-element transposition in Drosophila is regulated by tissue-specific alternative splicing of the P-element transposase pre-mRNA. In somatic cells, the P-element somatic inhibitor (PSI) protein binds to exon 3 of the pre-mRNA and recruits U1 small nuclear ribonucleoprotein (snRNP) to the F1 pseudo-splice site. This abrogates binding of U1 snRNP to the genuine 5' splice site, thereby preventing excision of the third intron. Two homologous short sequences, referred to as the A and B boxes, near the C terminus of PSI bind to U1-70k protein within U1 snRNP. We have now mapped the AB box-binding site of U1-70k to a short proline-rich sequence at the C terminus. Our NMR study shows that the B box forms an anti-parallel helical hairpin in which four highly conserved aromatic residues form a cluster on one face of the first helix. This hydrophobic cluster interacts extensively with the proline-rich region of the U1-70k protein.

MeSH terms

  • Alternative Splicing*
  • Amino Acid Sequence
  • Base Sequence
  • Binding Sites
  • Drosophila Proteins / metabolism*
  • Drosophila Proteins / physiology
  • Exons
  • Introns
  • Magnetic Resonance Spectroscopy
  • Nuclear Proteins / metabolism*
  • Nuclear Proteins / physiology
  • Protein Binding
  • RNA Precursors
  • RNA-Binding Proteins / metabolism*
  • RNA-Binding Proteins / physiology
  • Ribonucleoprotein, U1 Small Nuclear / metabolism*
  • Transposases / genetics*


  • Drosophila Proteins
  • Nuclear Proteins
  • PSI protein, Drosophila
  • RNA Precursors
  • RNA-Binding Proteins
  • Ribonucleoprotein, U1 Small Nuclear
  • Transposases