Dual roles for the Mss116 cofactor during splicing of the ai5γ group II intron

Nucleic Acids Res. 2010 Oct;38(19):6602-9. doi: 10.1093/nar/gkq530. Epub 2010 Jun 16.


The autocatalytic group II intron ai5γ from Saccharomyces cerevisiae self-splices under high-salt conditions in vitro, but requires the assistance of the DEAD-box protein Mss116 in vivo and under near-physiological conditions in vitro. Here, we show that Mss116 influences the folding mechanism in several ways. By comparing intron precursor RNAs with long (∼300 nt) and short (∼20 nt) exons, we observe that long exon sequences are a major obstacle for self-splicing in vitro. Kinetic analysis indicates that Mss116 not only mitigates the inhibitory effects of long exons, but also assists folding of the intron core. Moreover, a mutation in conserved Motif III that impairs unwinding activity (SAT → AAA) only affects the construct with long exons, suggesting helicase unwinding during exon unfolding, but not in intron folding. Strong parallels between Mss116 and the related protein Cyt-19 from Neurospora crassa suggest that these proteins form a subclass of DEAD-box proteins that possess a versatile repertoire of diverse activities for resolving the folding problems of large RNAs.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / metabolism*
  • Exons
  • Fungal Proteins / metabolism
  • Introns*
  • Kinetics
  • Mutation
  • Nucleic Acid Conformation
  • RNA Splicing*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Salts / chemistry


  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • Salts
  • MSS116 protein, S cerevisiae
  • DEAD-box RNA Helicases