title: The putative GTPase encoded by MTG3 functions in a novel pathway for regulating assembly of the small subunit of yeast mitochondrial ribosomes.
abstract: Very little is known about biogenesis of mitochondrial ribosomes. The GTPases encoded by the nuclear MTG1 and MTG2 genes of Saccharomyces cerevisiae have been reported to play a role in assembly of the ribosomal 54 S subunit. In the present study biochemical screens of a collection of respiratory deficient yeast mutants have enabled us to identify a third gene essential for expression of mitochondrial ribosomes. This gene codes for a member of the YqeH family of GTPases, which we have named MTG3 in keeping with the earlier convention. Mutations in MTG3 cause the accumulation of the 15 S rRNA precursor, previously shown to have an 80-nucleotide 5' extension. Sucrose gradient sedimentation of mitochondrial ribosomes from temperature-sensitive mtg3 mutants grown at the permissive and restrictive temperatures, combined with immunobloting with subunit-specific antibodies, indicate that Mtg3p is required for assembly of the 30 S but not 54 S ribosomal subunit. The respiratory deficient growth phenotype of an mtg3 null mutant is partially rescued by overexpression of the Mrpl4p constituent located at the peptide exit site of the 54 S subunit. The rescue is accompanied by an increase in processed 15 S rRNA. This suggests that Mtg3p and Mrpl4p jointly regulate assembly of the small subunit by modulating processing of the 15 S rRNA precursor.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Paul
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Alushin
authors.forename: Mario H
authors.initials: MH
authors.lastname: Barros
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Rak
authors.forename: Alexander
authors.initials: A
authors.lastname: Tzagoloff
mesh_terms: D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation; D012335:RNA, Ribosomal / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D020558:GTP Phosphohydrolases