The BTB domain is a protein-protein interaction motif that is found throughout eukaryotes. It determines a unique tri-dimensional fold with a large interaction surface. The exposed residues are highly variable and can permit dimerization and oligomerization, as well as interaction with a number of other proteins. BTB-containing proteins are numerous and control cellular processes that range from actin dynamics to cell-cycle regulation. Here, we review findings in the field of transcriptional regulation to illustrate how the high variability of the BTB has allowed related transcription factors to evolve different functional abilities. We then report how recent work has showed that, in spite of their high sequence divergence and apparently unrelated functions, many BTB-containing proteins have at least one shared role: the recruitment of degradation targets to E3 ubiquitin ligase complexes. Taken together, these findings illustrate diverse and convergent functions of a versatile protein-protein interaction domain.

Recently, a new type of hybrid resulting from the hybridization between Saccharomyces cerevisiae and Saccharomyces kudriavzevii was described. These strains exhibit physiological properties of potential biotechnological interest. A preliminary characterization of these hybrids showed a trend to reduce the S. kudriavzevii fraction of the hybrid genome. We characterized the genomic constitution of several wine S. cerevisiae ؋ S. kudriavzevii strains by using a combined approach based on the restriction fragment length polymorphism analysis of gene regions, comparative genome hybridizations with S. cerevisiae DNA arrays, ploidy analysis, and gene dose determination by quantitative real-time PCR. The high similarity in the genome structures of the S. cerevisiae ؋ S. kudriavzevii hybrids under study indicates that they originated from a single hybridization event. After hybridization, the hybrid genome underwent extensive chromosomal rearrangements, including chromosome losses and the generation of chimeric chromosomes by the nonreciprocal recombination between homeologous chromosomes. These nonreciprocal recombinations between homeologous chromosomes occurred in highly conserved regions, such as Ty long terminal repeats (LTRs), rRNA regions, and conserved protein-coding genes. This study supports the hypothesis that chimeric chromosomes may have been generated by a mechanism similar to the recombination-mediated chromosome loss acting during meiosis in Saccharomyces hybrids. As a result of the selective processes acting during fermentation, hybrid genomes maintained the S. cerevisiae genome but reduced the S. kudriavzevii fraction.The genus Saccharomyces consists of seven biological species: S. arboricolus, S. bayanus, S. cariocanus, S. cerevisiae, S. kudriavzevii, S. mikatae, and S. paradoxus (29, 59) and the partially allotetraploid species S. pastorianus (46, 58).The hybrid species S. pastorianus, restricted to lager brewing environments, arose from two or more natural hybridization events between S. cerevisiae and a S. bayanus-like yeast (7,16,28,46). Recent studies of S. bayanus have also revealed the hybrid nature of certain strains of this species, which has subsequently been subdivided into two groups, S. bayanus var. bayanus, containing a variety of hybrid strains, and S. bayanus var. uvarum, also referred to as S. uvarum, that contains nonhybrid strains (45,46). New hybrids of other species from the genus Saccharomyces have recently been described. Hybrid yeasts of S. cerevisiae and S. kudriavzevii have been characterized among wine (6,20,33) and brewing yeasts (21); even triple hybrids of S. cerevisiae, S. bayanus, and S. kudriavzevii have been identified (20,41).The first natural Saccharomyces interspecific hybrid identified, the lager brewing yeast S. pastorianus (S. carlsbergensis) (42, 57), has become one of the most investigated types of yeast hybrids. The genome structure of these hybrids has been examined by competitive array comparative genome hybridization (aCGH) (5, 16, 28), complete genome seq...

BackgroundWine Saccharomyces cerevisiae strains, adapted to anaerobic must fermentations, suffer oxidative stress when they are grown under aerobic conditions for biomass propagation in the industrial process of active dry yeast production. Oxidative metabolism of sugars favors high biomass yields but also causes increased oxidation damage of cell components. The overexpression of the TRX2 gene, coding for a thioredoxin, enhances oxidative stress resistance in a wine yeast strain model. The thioredoxin and also the glutathione/glutaredoxin system constitute the most important defense against oxidation. Trx2p is also involved in the regulation of Yap1p-driven transcriptional response against some reactive oxygen species.ResultsLaboratory scale simulations of the industrial active dry biomass production process demonstrate that TRX2 overexpression increases the wine yeast final biomass yield and also its fermentative capacity both after the batch and fed-batch phases. Microvinifications carried out with the modified strain show a fast start phenotype derived from its enhanced fermentative capacity and also increased content of beneficial aroma compounds. The modified strain displays an increased transcriptional response of Yap1p regulated genes and other oxidative stress related genes. Activities of antioxidant enzymes like Sod1p, Sod2p and catalase are also enhanced. Consequently, diminished oxidation of lipids and proteins is observed in the modified strain, which can explain the improved performance of the thioredoxin overexpressing strain.ConclusionsWe report several beneficial effects of overexpressing the thioredoxin gene TRX2 in a wine yeast strain. We show that this strain presents an enhanced redox defense. Increased yield of biomass production process in TRX2 overexpressing strain can be of special interest for several industrial applications.

Physiological capabilities and fermentation performance of Saccharomyces cerevisiae strains to be employed during industrial wine fermentations are critical for the quality of the final product. During the process of biomass propagation, yeast cells are dynamically exposed to a mixed and interrelated group of known stresses such as osmotic, oxidative, thermic, and/or starvation. These stressing conditions can dramatically affect the parameters of the fermentation process and the technological abilities of the yeast, e.g., the biomass yield and its fermentative capacity. Although a good knowledge exists of the behavior of S. cerevisiae under laboratory conditions, insufficient knowledge is available about yeast stress responses under the specific media and growth conditions during industrial processes. We performed growth experiments using bench-top fermentors and employed a molecular marker approach (changes in expression levels of five stress-related genes) to investigate how the cells respond to environmental changes during the process of yeast biomass production. The data show that in addition to the general stress response pathway, using the HSP12 gene as a marker, other specific stress response pathways were induced, as indicated by the changes detected in the mRNA levels of two stress-related genes, GPD1 and TRX2. These results suggest that the cells were affected by osmotic and oxidative stresses, demonstrating that these are the major causes of the stress response throughout the process of wine yeast biomass production.