Dual roles for the Mss116 cofactor during splicing of the ai5γ group II intron.
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.
Zingler
Nora
N
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
Solem
Amanda
A
Pyle
Anna Marie
AM
D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D005091:Exons; D005656:Fungal Proteins / Q000378:metabolism; D007438:Introns; D007700:Kinetics; D009154:Mutation; D009690:Nucleic Acid Conformation; D012326:RNA Splicing; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D012492:Salts / Q000737:chemistry
D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D012492:Salts; C058150:MSS116 protein, S cerevisiae; D053487:DEAD-box RNA Helicases