title: Mitochondrial Ribosomal Protein L12 Is Required for POLRMT Stability and Exists as Two Forms Generated by Alternative Proteolysis during Import.
abstract: To translate the 13 mtDNA-encoded mRNAs involved in oxidative phosphorylation (OXPHOS), mammalian mitochondria contain a dedicated set of ribosomes comprising rRNAs encoded by the mitochondrial genome and mitochondrial ribosomal proteins (MRPs) that are encoded by nuclear genes and imported into the matrix. In addition to their role in the ribosome, several MRPs have auxiliary functions or have been implicated in other cellular processes like cell cycle regulation and apoptosis. For example, we have shown that human MRPL12 binds and activates mitochondrial RNA polymerase (POLRMT), and hence has distinct functions in the ribosome and mtDNA transcription. Here we provide concrete evidence that there are two mature forms of mammalian MRPL12 that are generated by a two-step cleavage during import, involving efficient cleavage by mitochondrial processing protease and a second inefficient or regulated cleavage by mitochondrial intermediate protease. We also show that knock-down of MRPL12 by RNAi results in instability of POLRMT, but not other primary mitochondrial transcription components, and a corresponding decrease in mitochondrial transcription rates. Knock-down of MRPL10, the binding partner of MRPL12 in the ribosome, results in selective degradation of the mature long form of MRPL12, but has no effect on POLRMT. We propose that the two forms of MRPL12 are involved in homeostatic regulation of mitochondrial transcription and ribosome biogenesis that likely contribute to cell cycle, growth regulation, and longevity pathways to which MRPL12 has been linked.
authors.affiliation: From the Departments of Pathology and.
authors.forename: Jessica
authors.initials: J
authors.lastname: Nouws
authors.affiliation: From the Departments of Pathology and.
authors.forename: Arvind V
authors.initials: AV
authors.lastname: Goswami
authors.affiliation: From the Departments of Pathology and the Department of Chemistry, Linfield College, McMinnville, Oregon 97128, and.
authors.forename: Megan
authors.initials: M
authors.lastname: Bestwick
authors.affiliation: From the Departments of Pathology and the Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
authors.forename: Beverly Jo
authors.initials: BJ
authors.lastname: McCann
authors.affiliation: From the Departments of Pathology and.
authors.forename: Yulia V
authors.initials: YV
authors.lastname: Surovtseva
authors.affiliation: From the Departments of Pathology and Genetics, Yale School of Medicine, New Haven, Connecticut 06520-8023, gerald.shadel@yale.edu.
authors.forename: Gerald S
authors.initials: GS
authors.lastname: Shadel
mesh_terms: D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000378:metabolism; D055550:Protein Stability; D021381:Protein Transport; D059748:Proteolysis; D012269:Ribosomal Proteins / Q000737:chemistry / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D024101:Mitochondrial Proteins; D020033:Protein Isoforms; D012269:Ribosomal Proteins; C016700:ribosomal protein L7-L12; D012321:DNA-Directed RNA Polymerases; C519567:POLRMT protein, human
keywords: MIP; MRPL12; POLRMT; RNA polymerase; mitochondria; mitochondrial import; mtDNA; proteolysis; ribosome; transcription