RESUMEN
Mutations affecting the RNA sequence of the first 10 codons of the Saccharomyces cerevisiae mitochondrial gene COX2 strongly reduce translation of the mRNA, which encodes the precursor of cytochrome c oxidase subunit II. A dominant chromosomal mutation that suppresses these defects is an internal in-frame deletion of 67 codons from the gene YDR494w. Wild-type YDR494w encodes a 361-residue polypeptide with no similarity to proteins of known function. The epitope-tagged product of this gene, now named RSM28, is both peripherally associated with the inner surface of the inner mitochondrial membrane and soluble in the matrix. Epitope-tagged Rsm28p from Triton X-100-solubilized mitochondria sedimented with the small subunit of mitochondrial ribosomes in a sucrose gradient containing 500 mM NH4Cl. Complete deletion of RSM28 caused only a modest decrease in growth on nonfermentable carbon sources in otherwise wild-type strains and enhanced the respiratory defect of the suppressible cox2 mutations. The rsm28 null mutation also reduced translation of an ARG8m reporter sequence inserted at the COX1, COX2, and COX3 mitochondrial loci. We tested the ability of RSM28-1 to suppress a variety of cox2 and cox3 mutations and found that initiation codon mutations in both genes were suppressed. We conclude that Rsm28p is a dispensable small-subunit mitochondrial ribosomal protein previously undetected in systematic investigations of these ribosomes, with a positive role in translation of several mitochondrial mRNAs.
Asunto(s)
ADN Mitocondrial , Complejo IV de Transporte de Electrones/genética , Proteínas Mitocondriales/metabolismo , Biosíntesis de Proteínas , Subunidades de Proteína/metabolismo , Proteínas Ribosómicas/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Alelos , Complejo IV de Transporte de Electrones/metabolismo , Proteínas Mitocondriales/genética , Mutación , Señales de Clasificación de Proteína/genética , Subunidades de Proteína/genética , ARN Mensajero/metabolismo , Proteínas Ribosómicas/genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genéticaRESUMEN
PerR is a ferric uptake repressor (Fur) homolog that functions as the central regulator of the inducible peroxide stress response in Bacillus subtilis. PerR has been previously demonstrated to regulate the mrgA, katA, ahpCF, hemAXCDBL, and zosA genes. We now demonstrate that PerR also mediates both the repression of its own gene and that of fur. Whereas PerR-mediated repression of most target genes can be elicited by either manganese or iron, repression of perR and fur is selective for manganese. Genetic studies indicate that repression of PerR regulon genes by either manganese or iron requires PerR and is generally independent of Fur. Indeed, in a fur mutant, iron-mediated repression is enhanced. Unexpectedly, repression of the fur gene by manganese appears to require both PerR and Fur, but only PerR binds to the fur regulatory region in vitro. The fur mutation appears to act indirectly by affecting cellular metal ion pools and thereby affecting PerR-mediated repression. While many components of the perR regulon are strongly induced by hydrogen peroxide, little, if any, induction of fur and perR could be demonstrated. Thus, not all components of the PerR regulon are components of the peroxide stimulon. We suggest that PerR exists in distinct metallated forms that differ in DNA target selectivity and in sensitivity to oxidation. This model is supported by the observation that the metal ion composition of the growth medium can greatly influence the transcriptional response of the various PerR regulon genes to hydrogen peroxide.