title: Recruitment of intron-encoded and co-opted proteins in splicing of the bI3 group I intron RNA.
abstract: 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.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA.
authors.forename: Gurminder S
authors.initials: GS
authors.lastname: Bassi
authors.forename: Daniela M
authors.initials: DM
authors.lastname: de Oliveira
authors.forename: Malcolm F
authors.initials: MF
authors.lastname: White
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Weeks
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002499:Centrifugation, Density Gradient; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D007438:Introns; D007700:Kinetics; D024101:Mitochondrial Proteins; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012326:RNA Splicing; D016601:RNA-Binding Proteins; D016914:Ribonuclease H / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors
chemical_list: C078505:MRS1 protein, S cerevisiae; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins; D016914:Ribonuclease H