title: Disruption of ribosome assembly in yeast blocks cotranscriptional pre-rRNA processing and affects the global hierarchy of ribosome biogenesis.
abstract: In higher eukaryotes, pre-rRNA processing occurs almost exclusively post-transcriptionally. This is not the case in rapidly dividing yeast, as the majority of nascent pre-rRNAs are processed cotranscriptionally, with cleavage at the A2 site first releasing a pre-40S ribosomal subunit followed by release of a pre-60S ribosomal subunit upon transcription termination. Ribosome assembly is driven in part by hierarchical association of assembly factors and r-proteins. Groups of proteins are thought to associate with pre-ribosomes cotranscriptionally during early assembly steps, whereas others associate later, after transcription is completed. Here we describe a previously uncharacterized phenotype observed upon disruption of ribosome assembly, in which normally late-binding proteins associate earlier, with pre-ribosomes containing 35S pre-rRNA. As previously observed by many other groups, we show that disruption of 60S subunit biogenesis results in increased amounts of 35S pre-rRNA, suggesting that a greater fraction of pre-rRNAs are processed post-transcriptionally. Surprisingly, we found that early pre-ribosomes containing 35S pre-rRNA also contain proteins previously thought to only associate with pre-ribosomes after early pre-rRNA processing steps have separated maturation of the two subunits. We believe the shift to post-transcriptional processing is ultimately due to decreased cellular division upon disruption of ribosome assembly. When cells are grown under stress or to high density, a greater fraction of pre-rRNAs are processed post-transcriptionally and follow an alternative processing pathway. Together, these results affirm the principle that ribosome assembly occurs through different, parallel assembly pathways and suggest that there is a kinetic foot-race between the formation of protein binding sites and pre-rRNA processing events.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA The Center for Nucleic Acids Science and Technology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, California 95064, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Talkish
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA The Center for Nucleic Acids Science and Technology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Biedka
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA The Center for Nucleic Acids Science and Technology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Jelena
authors.initials: J
authors.lastname: Jakovljevic
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Jingyu
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Lan
authors.initials: L
authors.lastname: Tang
authors.affiliation: Department of Biological Chemistry, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Strahler
authors.affiliation: Department of Biological Chemistry, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Andrews
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Janine R
authors.initials: JR
authors.lastname: Maddock
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA The Center for Nucleic Acids Science and Technology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: John L
authors.initials: JL
authors.lastname: Woolford
mesh_terms: D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D015003:Yeasts / Q000235:genetics / Q000378:metabolism*
chemical_list: D012322:RNA Precursors; D012331:RNA, Fungal
keywords: cotranscriptional assembly; hierarchical assembly; pre-rRNA processing; pre-ribosomes; yeast ribosome assembly