Developing functional foods to improve the quality of life for elderly people has great economic and social impact. Searching for and validating ingredients with in vivo antioxidant effects is one of the key steps in developing this kind of food. Here we describe the combined use of simple biological models and transcriptomics to define the functional intracellular molecular targets of a polyphenol-enriched cocoa powder. Cocoa powder supplemented culture medium led to increased resistance to oxidative stress, in both the budding yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans, and, in the latter, lifespan was also increased. These effects are fully dependent on the polyphenols present in the cocoa powder and on the sirtuins Hst3 (yeast) and SIR-2.1 (worm). The transcription factor DAF-16 also plays an important role in the case of the nematode, indicating that the insulin/IGF-1 (insulin-like growth factor) signaling pathway is related with the antioxidative effect of cocoa polyphenols. All in all, these results confirm that this polyphenol-enriched cocoa powder, with antioxidant activity, has great potential use as a functional food ingredient for elderly people. Furthermore, this work reveals the value of using simple biological models to screen for compounds that are of interest for the food and pharmacological industry.

Saccharomyces cerevisiae is the most widely used yeast in industrial/commercial food and beverage production and is even consumed as a nutritional supplement. Various cases of fungemia caused by this yeast species in severely debilitated traumatized or immune-deficient patients have been reported in recent years, suggesting that this species could be an opportunistic pathogen in such patients. To determine whether the industrial S. cerevisiae strains can be included in this virulent group of strains, we carried out a comparative study between clinical and industrial yeasts based on the various phenotypic traits associated with pathogenicity in two other yeast species (Candida albicans and Cryptococcus neoformans). The majority of the clinical isolates were found to secrete higher levels of protease and phospholipase, grow better at 42 degrees C and show strong pseudohyphal growth relative to industrial yeasts. However three industrial yeast strains, one commercial wine strain, baker's yeast and one commercial strain of S. cerevisiae (var. boulardii), were exceptions and based on their physiological traits these yeasts would appear to be related to clinical strains.

No abstract

Iron is an essential micronutrient for all eukaryotic organisms because it participates as a redox-active cofactor in many biological processes, including DNA replication and repair. Eukaryotic ribonucleotide reductases (RNRs) are Fe-dependent enzymes that catalyze deoxyribonucleoside diphosphate (dNDP) synthesis. We show here that the levels of the Sml1 protein, a yeast RNR large-subunit inhibitor, specifically decrease in response to both nutritional and genetic Fe deficiencies in a Dun1-dependent but Mec1/Rad53-and Aft1-independent manner. The decline of Sml1 protein levels upon Fe starvation depends on Dun1 forkheadassociated and kinase domains, the 26S proteasome, and the vacuolar proteolytic pathway. Depletion of core components of the mitochondrial iron-sulfur cluster assembly leads to a Dun1-dependent diminution of Sml1 protein levels. The physiological relevance of Sml1 downregulation by Dun1 under low-Fe conditions is highlighted by the synthetic growth defect observed between dun1⌬ and fet3⌬ fet4⌬ mutants, which is rescued by SML1 deletion. Consistent with an increase in RNR function, Rnr1 protein levels are upregulated upon Fe deficiency. Finally, dun1⌬ mutants display defects in deoxyribonucleoside triphosphate (dNTP) biosynthesis under low-Fe conditions. Taken together, these results reveal that the Dun1 checkpoint kinase promotes RNR function in response to Fe starvation by stimulating Sml1 protein degradation. Ribonucleotide reductase (RNR) is an essential enzyme that catalyzes the de novo synthesis of deoxyribonucleoside diphosphates (dNDPs), which are the precursors for DNA replication and repair. Eukaryotic RNRs are comprised of ␣ and ␤ subunits that form an active quaternary structure, (␣ 2 ) 3 (␤ 2 ) m , where m is 1 or 3. ␣ 2 , referred to as the large or R1 subunit, contains the catalytic and allosteric sites, and ␤ 2 , known as the small or R2 subunit, harbors a diferric center that is responsible for generating and keeping a tyrosyl radical required for catalysis (reviewed in references 1 to 3). In the budding yeast Saccharomyces cerevisiae, the large R1 subunit is formed by an Rnr1 homodimer and the small R2 subunit is composed of an Rnr2-Rnr4 heterodimer (reviewed in reference 4). Eukaryotic cells tightly control RNR activity to achieve adequate and balanced deoxyribonucleoside triphosphate (dNTP) pools that ensure accurate DNA synthesis and genomic integrity. In response to DNA damage or DNA replication stress or when cells enter S phase of the cell cycle, the yeast Mec1/Rad53/Dun1 checkpoint kinase cascade activates RNR function (reviewed in reference 4). Briefly, genotoxic stress activates Mec1, which phosphorylates and enhances Rad53 kinase activity (5, 6). A diphosphothreonine motif in hyperphosphorylated Rad53 protein is subsequently recognized by Dun1's forkhead-associated (FHA) domain, leading to Rad53-mediated phosphorylation and activation of Dun1 kinase (7-11), which promotes RNR function through multiple mechanisms. One mechanism involves the transcriptional repressor Crt1,...