title: Mechanism for Aar2p function as a U5 snRNP assembly factor.
abstract: Little is known about how particle-specific proteins are assembled on spliceosomal small nuclear ribonucleoproteins (snRNPs). Brr2p is a U5 snRNP-specific RNA helicase required for spliceosome catalytic activation and disassembly. In yeast, the Aar2 protein is part of a cytoplasmic precursor U5 snRNP that lacks Brr2p and is replaced by Brr2p in the nucleus. Here we show that Aar2p and Brr2p bind to different domains in the C-terminal region of Prp8p; Aar2p interacts with the RNaseH domain, whereas Brr2p interacts with the Jab1/MPN domain. These domains are connected by a long, flexible linker, but the Aar2p-RNaseH complex sequesters the Jab1/MPN domain, thereby preventing binding by Brr2p. Aar2p is phosphorylated in vivo, and a phospho-mimetic S253E mutation in Aar2p leads to disruption of the Aar2p-Prp8p complex in favor of the Brr2p-Prp8p complex. We propose a model in which Aar2p acts as a phosphorylation-controlled U5 snRNP assembly factor that regulates the incorporation of the particle-specific Brr2p. The purpose of this regulation may be to safeguard against nonspecific RNA binding to Prp8p and/or premature activation of Brr2p activity.
authors.affiliation: Fachbereich Biologie/Chemie/Pharmazie, Abteilung Strukturbiochemie, Freie Universität Berlin, D-14195 Berlin, Germany;
authors.forename: Gert
authors.initials: G
authors.lastname: Weber
authors.forename: Vanessa F
authors.initials: VF
authors.lastname: Cristão
authors.forename: Flavia
authors.initials: F
authors.lastname: de L Alves
authors.forename: Karine F
authors.initials: KF
authors.lastname: Santos
authors.forename: Nicole
authors.initials: N
authors.lastname: Holton
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.forename: Jean D
authors.initials: JD
authors.lastname: Beggs
authors.forename: Markus C
authors.initials: MC
authors.lastname: Wahl
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020365:RNA Helicases / Q000737:chemistry / Q000378:metabolism; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry / Q000378:metabolism; D017415:Ribonucleoprotein, U5 Small Nuclear / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C440573:Aar2p protein, S cerevisiae; D033942:Adaptor Proteins, Vesicular Transport; D009687:Nuclear Proteins; C077018:PRP8 protein, S cerevisiae; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017415:Ribonucleoprotein, U5 Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; C104158:BRR2 protein, S cerevisiae; D020365:RNA Helicases