title: Coordinated Ribosomal ITS2 RNA Processing by the Las1 Complex Integrating Endonuclease, Polynucleotide Kinase, and Exonuclease Activities.
abstract: The rapidly evolving internal transcribed spacer 2 (ITS2) in the pre-ribosomal RNA is one of the most commonly applied phylogenetic markers at species and genus level. Yet, during ribosome biogenesis ITS2 is removed in all eukaryotes by a common, but still unknown, mechanism. Here we describe the existence of an RNA processome, assembled from four conserved subunits, Las1-Grc3-Rat1-Rai1, that carries all the necessary RNA processing enzymes to mediate coordinated ITS2 rRNA removal. Las1 is the long-sought-after endonuclease cleaving 27SB pre-rRNA at site C2 to yield a 5'-OH end at the 26S pre-rRNA and 2',3' cyclic phosphate at the 3' end of 7S pre-rRNA. Subsequently, polynucleotide kinase Grc3 catalyzes ATP-dependent 5'-OH phosphorylation of 26S pre-rRNA, which in turn enables Rat1-Rai1 exonuclease to generate 25S' pre-rRNA. ITS2 processing is reminiscent of tRNA splicing, but instead of subsequent tRNA ligation, the Las1 complex carries along an exonuclease tool to degrade the ITS2 rRNA.
authors.affiliation: Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, Heidelberg 69120, Germany.
authors.forename: Lisa
authors.initials: L
authors.lastname: Gasse
authors.affiliation: Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, Heidelberg 69120, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Flemming
authors.affiliation: Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, Heidelberg 69120, Germany. Electronic address: ed.hurt@bzh.uni-heidelberg.de.
authors.forename: Ed
authors.initials: E
authors.lastname: Hurt
mesh_terms: D021903:DNA, Ribosomal Spacer / Q000378:metabolism*; D005095:Exoribonucleases / Q000378:metabolism; D046912:Multiprotein Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D012331:RNA, Fungal / Q000378:metabolism; D012335:RNA, Ribosomal / Q000378:metabolism; D016601:RNA-Binding Proteins; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D021903:DNA, Ribosomal Spacer; C098171:LAS1 protein, S cerevisiae; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D012331:RNA, Fungal; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; C473024:Rai1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C075577:RAT1 protein, S cerevisiae; D005095:Exoribonucleases