Recruitment of intron-encoded and co-opted proteins in splicing of the bI3 group I intron RNA

Proc Natl Acad Sci U S A. 2002 Jan 8;99(1):128-33. doi: 10.1073/pnas.012579299. Epub 2002 Jan 2.


Detectable splicing by the Saccharomyces cerevisiae mitochondrial bI3 group I intron RNA in vitro is shown to require both an intron-encoded protein, the bI3 maturase, and the nuclear-encoded protein, Mrs1. Both proteins bind independently to the bI3 RNA. The bI3 maturase binds as a monomer, whereas Mrs1 is a dimer in solution that assembles as two dimers, cooperatively, on the RNA. The active six-subunit complex has a molecular mass of 420 kDa, splices with a k(cat) of 0.3 min(-1), and binds the guanosine nucleophile with an affinity comparable to other group I introns. The functional bI3 maturase domain is translated from within the RNA that encodes the intron, has evolved a high-affinity RNA-binding activity, and is a member of the LAGLIDADG family of DNA endonucleases, but appears to have lost DNA cleavage activity. Mrs1 is a divergent member of the RNase H fold superfamily of dimeric DNA junction-resolving enzymes that also appears to have lost its nuclease activity and now functions as a tetramer in RNA binding. Thus, the bI3 ribonucleoprotein is the product of a process in which a once-catalytically active RNA now obligatorily requires two facilitating protein cofactors, both of which are compromised in their original functions.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Centrifugation, Density Gradient
  • Dimerization
  • Dose-Response Relationship, Drug
  • Introns*
  • Kinetics
  • Mitochondrial Proteins
  • Models, Biological
  • Models, Genetic
  • Molecular Sequence Data
  • Nuclear Proteins / genetics*
  • Protein Binding
  • Protein Structure, Tertiary
  • RNA Splicing*
  • RNA-Binding Proteins
  • Ribonuclease H / metabolism
  • Ribonucleoproteins / metabolism
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / physiology
  • Saccharomyces cerevisiae Proteins*
  • Time Factors


  • MRS1 protein, S cerevisiae
  • Mitochondrial Proteins
  • Nuclear Proteins
  • RNA-Binding Proteins
  • Ribonucleoproteins
  • Saccharomyces cerevisiae Proteins
  • Ribonuclease H