title: A single mutation in the 15S rRNA gene confers non sense suppressor activity and interacts with mRF1 the release factor in yeast mitochondria.
abstract: We have determined the nucleotide sequence of the mim3-1 mitochondrial ribosomal suppressor, acting on ochre mitochondrial mutations and one frameshift mutation inSaccharomyces cerevisiae. The 15s rRNA suppressor gene contains a G633 to C transversion. Yeast mitochondrial G633 corresponds to G517 of theE.coli15S rRNA, which is occupied by an invariant G in all known small rRNA sequences. Interestingly, this mutation has occurred at the same position as the known MSU1 mitochondrial suppressor which changes G633 to A. The suppressor mutation lies in a highly conserved region of the rRNA, known inE.colias the 530-loop, interacting with the S4, S5 and S12 ribosomal proteins. We also show an interesting interaction between the mitochondrial mim3-1 and the nuclear nam3-1 suppressors, both of which have the same action spectrum on mitochondrial mutations: nam3-1 abolishes the suppressor effect when present with mim3-1 in the same haploid cell. We discuss these results in the light of the nature of Nam3, identified by 1 as the yeast mitochondrial translation release factor. A hypothetical mechanism of suppression by "ribosome shifting" is also discussed in view of the nature of mutations suppressed and not suppressed.
authors.affiliation: Centre de Génétique Moléculaire, Laboratoire propre du C.N.R.S associé à l'Université Pierre et Marie Curie. CNRS F-91198 Gif-sur-Yvette cedex, France.
authors.forename: Ali
authors.initials: A
authors.lastname: Gargouri
authors.affiliation: Centre de Génétique Moléculaire, Laboratoire propre du C.N.R.S associé à l'Université Pierre et Marie Curie. CNRS F-91198 Gif-sur-Yvette cedex, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Macadré
authors.affiliation: Centre de Génétique Moléculaire, Laboratoire propre du C.N.R.S associé à l'Université Pierre et Marie Curie. CNRS F-91198 Gif-sur-Yvette cedex, France.
authors.forename: Jaga
authors.initials: J
authors.lastname: Lazowska
keywords: 15S rRNA; frame shift; informational suppressors; nonsense; yeast