title: Multiple forms of the U2 small nuclear ribonucleoprotein auxiliary factor U2AF subunits expressed in higher plants.
abstract: Requirements for intron recognition during pre-mRNA splicing in plants differ from those in vertebrates and yeast. Plant introns contain neither conserved branch points nor distinct 3' splice site-proximal polypyrimidine tracts characteristic of the yeast and vertebrate introns, respectively. However, they are strongly enriched in U residues throughout the intron, property essential for splicing. To understand the roles of different sequence elements in splicing, we are characterizing proteins involved in intron recognition in plants. In this work we show that Nicotiana plumbaginifolia, a dicotyledonous plant, contains two genes encoding different homologs of the large 50-65-kDa subunit of the polypyrimidine tract binding factor U2AF, characterized previously in animals and Schizosaccharomyces pombe. Both plant U2AF65 isoforms, referred to as NpU2AF65a and NpU2AF65b, support splicing of an adenovirus pre-mRNA in HeLa cell nuclear extracts depleted of the endogenous U2AF factor. Both proteins interact with RNA fragments containing plant introns and show affinity for poly(U) and, to a lesser extend, poly(C) and poly(G). The branch point or the 3' splice site regions do not contribute significantly to intron recognition by NpU2AF65. The existence of multiple isoforms of U2AF may be quite general in plants because two genes expressing U2AF65 have been identified in Arabidopsis, and different isoforms of the U2AF small subunit are expressed in rice.
authors.affiliation: Friedrich Miescher-Institut, CH-4002 Basel, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Domon
authors.forename: Z J
authors.initials: ZJ
authors.lastname: Lorković
authors.forename: J
authors.initials: J
authors.lastname: Valcárcel
authors.forename: W
authors.initials: W
authors.lastname: Filipowicz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics; D005982:Glutathione Transferase / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010947:Plants, Toxic; D012326:RNA Splicing; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000235:genetics*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000072668:Splicing Factor U2AF; D014026:Nicotiana / Q000235:genetics*
chemical_list: D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D017413:Ribonucleoprotein, U2 Small Nuclear; D012261:Ribonucleoproteins; D000072668:Splicing Factor U2AF; C000607494:U2AF2 protein, human; C000607495:Zrsr1 protein, mouse; D005982:Glutathione Transferase