Absence of mitochondrial translation control proteins extends life span by activating sirtuin-dependent silencing.

Altered mitochondrial functionality can extend organism life span, but the underlying mechanisms are obscure. Here we report that inactivating SOV1, a member of the yeast mitochondrial translation control (MTC) module, causes a robust Sir2-dependent extension of replicative life span in the absence of respiration and without affecting oxidative damage. We found that SOV1 interacts genetically with the cAMP-PKA pathway and the chromatin remodeling apparatus. Consistently, Sov1p-deficient cells displayed reduced cAMP-PKA signaling and an elevated, Sir2p-dependent, genomic silencing. Both increased silencing and life span extension in sov1Δ cells require the PKA/Msn2/4p target Pnc1p, which scavenges nicotinamide, a Sir2p inhibitor. Inactivating other members of the MTC module also resulted in Sir2p-dependent life span extension. The data demonstrate that the nuclear silencing apparatus senses and responds to the absence of MTC proteins and that this response converges with a pathway for life span extension elicited by reducing TOR signaling.

The coordinate regulation of multiple terminal oxidases by the Pseudomonas putida ANR global regulator.

Pseudomonas putida KT2440 contains a branched aerobic respiratory chain with multiple terminal oxidases. Their relative proportion varies according to environmental conditions. The role of the oxygen-responsive ANR global regulator on expression of these terminal oxidases was analysed. During exponential growth in a highly aerated complete medium, ANR activated expression of the Cbb3-1 terminal oxidase (equivalent to Pseudomonas aeruginosa Cbb3-2), but had little role on expression of other terminal oxidases. In early stationary phase, or under oxygen limitation, inactivation of the anr gene led to increased expression of the bo(3)-type cytochrome (Cyo) and cyanide-insensitive (CIO) terminal oxidases, and to a much lower expression of Cbb3-1. DNase I footprints identified ANR binding sites at the promoters for these oxidases. Their location suggests that ANR is a transcriptional activator of Cbb3-1 genes and a repressor of CIO genes, consistent with expression data. ANR binding sites at the promoter for Cyo genes suggests a complex regulation in combination with other factors. Therefore, ANR coordinates expression of Cyo, CIO and Cbb3-1, but does not influence cytochrome aa3 and Cbb3-2 terminal oxidases under the conditions analysed. Functional assays showed that Cyo has a leading role during aerobic exponential growth, while Cbb3-1 becomes very important in stationary phase.

Perspectives on the mitochondrial etiology of replicative aging in yeast.

In a now classical paper, Denham Harman suggested that free radicals produced during mitochondrial respiration cause cumulative oxidative damage, resulting in aging and age-related disorders and pathologies. Proponents of this hypothesis have focused their attention, not surprisingly, on mitochondria arguing that these organelles may serve as the biological clock for aging. Indeed, work on many models, including filamentous fungi, nematodes, and mammals have revealed that age-dependent reorganizations of the mitochondrial DNA (mtDNA) may play a central role in the aging of these organisms. Furthermore, genetic alterations of mitochondrial function may either shorten or extend life span. In this paper, we focus on the role of mitochondria in the replicative aging of yeast mother cells, whether this role of mitochondria is really a linked to altered ROS production and/or respiration, and highlight some important questions that remain to be answered.

Inactivation of the Pseudomonas putida cytochrome o ubiquinol oxidase leads to a significant change in the transcriptome and to increased expression of the CIO and cbb3-1 terminal oxidases.

Pseudomonas putida KT2440 contains a branched aerobic respiratory chain with several terminal oxidases. Inactivation of the cyo terminal ubiquinol oxidase has little effect on growth rate but is known to relieve the inhibition by global control that modulates induction of genes required to assimilate alkanes in cells growing in the presence of preferred carbon sources. We show that inactivation of other terminal oxidases has no effect on regulation of the alkane degradation pathway, which points to cyo as the oxidase that transmits a regulatory signal related to the activity of the electron transport chain. Using a genome-wide DNA microarray we found that inactivation of cyo has a significant effect on the transcriptome, supporting that it participates in global regulation of gene expression. Among the genes affected stand out those coding for transporters of organic acids, porins, transcriptional regulators and terminal oxidases. Real-time reverse transcription polymerase chain reaction (RT-PCR) showed that, in cells growing exponentially in a complete medium, the absence of cyo was compensated by increased expression of the cyanide-insensitive and cbb3-1 terminal oxidases, while cbb3-2 and aa3 oxidases remained unaffected. When cells enter into stationary phase cyo levels decrease and inhibition of the alkane degradation genes ceases. This was paralleled by upregulation of the cyanide-insensitive, cbb3-1, cbb3-2 and aa3 terminal oxidases. The results suggest that P. putida adapts the composition of the electron transport chain not only to optimize energy generation, but also to influence the transcriptome profile of the cell through global control of gene expression.