title: Overexpression of Upf1p compensates for mitochondrial splicing deficiency independently of its role in mRNA surveillance.
abstract: In yeast the UPF1, UPF2 and UPF3 genes encode three interacting factors involved in translation termination and nonsense-mediated mRNA decay (NMD). UPF1 plays a central role in both processes. In addition, UPF1 was originally isolated as a multicopy suppressor of mitochondrial splicing deficiency, and its deletion leads to an impairment in respiratory growth. Here, we provide evidence that inactivation of UPF2 or UPF3, like that of UPF1, leads to an impairment in respiratory competence, suggesting that their products, Upf1p, Upf2p and Upf3p, are equivalently involved in mitochondrial biogenesis. In addition, however, we show that only Upf1p acts as a multicopy suppressor of mitochondrial splicing deficiency, and its activity does not require either Upf2p or Upf3p. Mutations in the conserved cysteine- and histidine-rich regions and ATPase and helicase motifs of Upf1p separate the ability of Upf1p to complement the respiratory impairment of a Deltaupf1 strain from its ability to act as a multicopy suppressor of mitochondrial splicing deficiency, indicating that distinct pathways express these phenotypes. In addition, we show that, when overexpressed, Upf1p is not detected within mitochondria, suggesting that its role as multicopy suppressor of mitochondrial splicing deficiency is indirect. Furthermore, we provide evidence that cells overexpressing certain upf1 alleles accumulate a phosphorylated isoform of Upf1p. Altogether, these results indicate that overexpression of Upf1p compensates for mitochondrial splicing deficiency independently of its role in mRNA surveillance, which relies on Upf1p-Upf2p-Upf3p functional interplay.
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto di Biomembrane e Bioenergetica, Bari, Italy.
authors.forename: B
authors.initials: B
authors.lastname: de Pinto
authors.forename: R
authors.initials: R
authors.lastname: Lippolis
authors.forename: R
authors.initials: R
authors.lastname: Castaldo
authors.forename: N
authors.initials: N
authors.lastname: Altamura
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D004252:DNA Mutational Analysis; D020868:Gene Silencing; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation; D010101:Oxygen Consumption; D010443:Peptide Chain Termination, Translational; D010766:Phosphorylation; D014176:Protein Biosynthesis; D020365:RNA Helicases / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D012323:RNA Processing, Post-Transcriptional; D012326:RNA Splicing; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology; D013489:Suppression, Genetic; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C092470:NMD2 protein, S cerevisiae; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; C096360:UPF3 protein, S cerevisiae; C074151:NAM7 protein, S cerevisiae; D020365:RNA Helicases