RESUMEN
Expression of yeast mitochondrial genes depends on specific translational activators acting on the 5'-untranslated region of their target mRNAs. Mss51p is a translational factor for cytochrome c oxidase subunit 1 (COX1) mRNA and a key player in down-regulating Cox1p expression when subunits with which it normally interacts are not available. Mss51p probably acts on the 5'-untranslated region of COX1 mRNA to initiate translation and on the coding sequence itself to facilitate elongation. Mss51p binds newly synthesized Cox1p, an interaction that could be necessary for translation. To gain insight into the different roles of Mss51p on Cox1p biogenesis, we have analyzed the properties of a new mitochondrial protein, mp15, which is synthesized in mss51 mutants and in cytochrome oxidase mutants in which Cox1p translation is suppressed. The mp15 polypeptide is not detected in cox14 mutants that express Cox1p normally. We show that mp15 is a truncated translation product of COX1 mRNA whose synthesis requires the COX1 mRNA-specific translational activator Pet309p. These results support a key role for Mss51p in translationally regulating Cox1p synthesis by the status of cytochrome oxidase assembly.
Asunto(s)
Citocromos c1/biosíntesis , Regulación Enzimológica de la Expresión Génica , Regulación Fúngica de la Expresión Génica , Biosíntesis de Proteínas/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimología , Factores de Transcripción/metabolismo , Regiones no Traducidas 5'/metabolismo , Cloranfenicol/farmacología , Citocromos c1/genética , Proteínas de la Membrana/análisis , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Proteínas Mitocondriales , Mutación , Proteínas Nucleares/genética , Factores de Iniciación de Péptidos , Péptidos/análisis , Péptidos/genética , Péptidos/metabolismo , ARN Mensajero/metabolismo , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genética , Factores de Transcripción/genética , Transcripción Genética/genéticaRESUMEN
Mitochondrial dysfunction may play an important role in the pathogenic mechanism of Huntington's disease (HD). However, the exact mechanism by which mutated huntingtin could cause bioenergetic dysfunction is still unknown. We have constructed a stable inducible yeast model of HD by expressing a human huntingtin fragment containing a mutant polyglutamine tract of 103Q fused to green fluorescent protein (GFP), and a control expressing a wild-type 25Q domain fused to GFP in a wild-type strain. We showed that in yeast cells expressing 103Q, cell respiration was progressively reduced after 4-6 h of induction with galactose, down to 50% of the control after 10 h of induction. The cell respiration defect results from an alteration in the function and amount of mitochondrial respiratory chain complex II+III, in congruency to data obtained from postmortem brain of HD patients and from toxin models. In our model, the production of reactive oxygen species (ROS) is significantly enhanced in cells expressing 103Q. Quenching of ROS with resveratrol partially prevents the cell respiration defect. Mitochondrial morphology and distribution were also altered in cells expressing 103Q, probably resulting from the interaction of aggregates with portions of the mitochondrial web and from a progressive disruption of the actin cytoskeleton. We propose a mechanism for mitochondrial dysfunction in our yeast model of HD in which the interactions of misfolded/aggregated polyglutamine domains with the mitochondrial and actin networks lead to disturbances in mitochondrial distribution and function and to increase in ROS production. Oxidative damage could preferentially affect the stability and function of enzymes containing iron-sulfur clusters such as complexes II and III. Our yeast model represents a very useful paradigm to study mitochondrial physiology alterations in the pathogenic mechanism of HD.
