Heterologous complementation of theKlaacnull mutation ofKluyveromyces lactisby theSaccharomyces cerevisiae AAC3gene encoding the ADP/ATP carrier

Thanksgiving to Yeast, the HMGB Proteins History from Yeast to Cancer

Yeasts have been a part of human life since ancient times in the fermentation of many natural products used for food. In addition, in the 20th century, they became powerful tools to elucidate the functions of eukaryotic cells as soon as the techniques of molecular biology developed. Our molecular understandings of metabolism, cellular transport, DNA repair, gene expression and regulation, and the cell division cycle have all been obtained through biochemistry and genetic analysis using different yeasts. In this review, we summarize the role that yeasts have had in biological discoveries, the use of yeasts as biological tools, as well as past and on-going research projects on HMGB proteins along the way from yeast to cancer.

Kluyveromyces lactis: a suitable yeast model to study cellular defense mechanisms against hypoxia-induced oxidative stress

Studies about hypoxia-induced oxidative stress in human health disorders take advantage from the use of unicellular eukaryote models. A widely extended model is the fermentative yeast Saccharomyces cerevisiae. In this paper, we describe an overview of the molecular mechanisms induced by a decrease in oxygen availability and their interrelationship with the oxidative stress response in yeast. We focus on the differential characteristics between S. cerevisiae and the respiratory yeast Kluyveromyces lactis, a complementary emerging model, in reference to multicellular eukaryotes.

Gene responses to oxygen availability in Kluyveromyces lactis: an insight on the evolution of the oxygen-responding system in yeast

The whole-genome duplication (WGD) may provide a basis for the emergence of the very characteristic life style of Saccharomyces cerevisiae—its fermentation-oriented physiology and its capacity of growing in anaerobiosis. Indeed, we found an over-representation of oxygen-responding genes in the ohnologs of S. cerevisiae. Many of these duplicated genes are present as aerobic/hypoxic(anaerobic) pairs and form a specialized system responding to changing oxygen availability. HYP2/ANB1 and COX5A/COX5B are such gene pairs, and their unique orthologs in the ‘non-WGD’ Kluyveromyces lactis genome behaved like the aerobic versions of S. cerevisiae. ROX1 encodes a major oxygen-responding regulator in S. cerevisiae. The synteny, structural features and molecular function of putative KlROX1 were shown to be different from that of ROX1. The transition from the K. lactis-type ROX1 to the S. cerevisiae-type ROX1 could link up with the development of anaerobes in the yeast evolution. Bioinformatics and stochastic analyses of the Rox1p-binding site (YYYATTGTTCTC) in the upstream sequences of the S. cerevisiae Rox1p-mediated genes and of the K. lactis orthologs also indicated that K. lactis lacks the specific gene system responding to oxygen limiting environment, which is present in the ‘post-WGD’ genome of S. cerevisiae. These data suggested that the oxygen-responding system was born for the specialized physiology of S. cerevisiae.

Functional characterization of KlHAP1: a model to foresee different mechanisms of transcriptional regulation by Hap1p in yeasts

In this work we have cloned and characterized the Kluyveromyces lactis HAP1 gene and we have found that, contrary to data previously described for the homologous gene of Saccharomyces cerevisiae, i.) the function of this gene does not affect growth in media with carbon sources used by fermentative or respiratory pathways ii) in aerobiosis, KlHap1p is not a transcriptional activator of the expression of genes related to respiration, cholesterol biosynthesis or oxidative stress defence analyzed in this study. The comparison of homology between specific regions of ScHap1p and KlHap1p reveals that the dimerization domain is poorly conserved and we have verified that this domain, cloned in the two plasmids of the two hybrid system, does not reconstitute S. cerevisiae Gal4p activity. Since the COOH-terminal transcriptional activation domain of KlHap1p is active when fused to the Gal4p-DNA binding domain, we hypothesize that differences in the capacity to form dimers could contribute to allow different functions of the protein in K. lactis and S. cerevisiae. Transcriptional expression of KlHAP1 is dependent on oxygen availability, increasing its expression in hypoxia. Deletion of KlHAP1 increases the resistance to oxidative stress or cadmium and the induction of KlYAP1 and KlTSA1 by the addition of 0.5 mM H(2)O(2) is repressed by KlHap1p. These data are discussed in reference to the evolution of respiro-fermentative metabolism in yeasts.