Homologous recombination is an important biological process that occurs in all organisms and facilitates genome rearrangements and repair of DNA double-strand breaks. Eukaryotic Rad51 proteins (Rad51 sp or Rhp51 in fission yeast) are functional and structural homologs of bacterial RecA protein, an evolutionarily conserved protein that plays a key role in homologous pairing and strand exchange between homologous DNA molecules in vitro. Here we show that the fission yeast swi5 ؉ gene, which was originally identified as a gene required for normal mating-type switching, encodes a protein conserved among eukaryotes and is involved in a previously uncharacterized Rhp51 (Rad51 sp )-dependent recombination repair pathway that does not require the Rhp55͞57 (Rad55͞57 sp ) function. Protein interactions with both Swi5 and Rhp51 were found to be mediated by a domain common to Swi2 and Sfr1 (Swi five-dependent recombination repair protein 1, a previously uncharacterized protein with sequence similarity to the C-terminal part of Swi2). Genetic epistasis analyses suggest that the Swi5-Sfr1-Rhp51 interactions function specifically in DNA recombination repair, whereas the Swi5-Swi2-Rhp51 interactions may function, together with chromodomain protein Swi6 (HP1 homolog), in mating-type switching.D NA double-strand breaks (DSBs) are caused by DNAdamaging agents, such as ionizing irradiation, and also arise during normal DNA replication. These accidentally generated DSBs are critical genotoxic lesions in all organisms. However, the DSBs can be repaired efficiently by several cellular mechanisms that maintain genome stability. Homologous recombination is one of the most important pathways for DSB repair.Eukaryotic Rad51 protein is regarded as the structural and functional counterpart of the Escherichia coli RecA protein and plays a central role in homologous recombination in eukaryotic cells (1). Purified Rad51 forms nucleoprotein filaments, like RecA (2), and promotes homologous pairing and strand exchange between homologous DNA strands in vitro (3, 4). However, eukaryotes possess additional RecA-like proteins such as Rad55 sc ͞ Rhp55 (Rad55 sp ) and Rad57 sc ͞Rhp57 (Rad57 sp ) in Saccharomyces cerevisiae and Schizosaccharomyces pombe and Rad51B, Rad51C, Rad51D, Xrcc2, and Xrcc3 in vertebrates (1).Biochemical studies have demonstrated that these RecA paralogs stimulate Rad51-mediated strand exchange (1, 5, 6). Rad55 (Rhp55) and Rad57 (Rhp57) form heterodimers and bind to Rad51 (Rhp51) (7,8). Null mutants of the S. pombe rhp51 gene are hypersensitive to DNA-damaging agents, and rhp51 mutations are epistatic to rhp55 or rhp57 mutations. In addition, paralog mutants are cold-sensitive, and overexpression of Rad51 (Rhp51) partially suppresses their DNA repair defects (9-12). Furthermore, the formation of Rhp51 foci in irradiated S. pombe cells depends on the rhp55 function (13). The dependence of Rad51 foci on paralogs has also been demonstrated in S. cerevisiae (14) and in chicken DT40 cells (12,15). These observations are consistent wi...

Candidiasis are life-threatening systemic fungal diseases, especially of gastro intestinal track, skin and mucous membranes lining various body cavities like the nostrils, the mouth, the lips, the eyelids, the ears or the genital area. Due to increasing resistance of candidiasis to existing drugs, it is very important to look for new strategies helping the treatment of such fungal diseases. One promising strategy is the use of the probiotic microorganisms, which when administered in adequate amounts confer a health benefit. Such a probiotic microorganism is yeast Saccharomyces boulardii, a close relative of baker yeast. Saccharomyces boulardii cells and their extract affect the virulence factors of the important human fungal pathogen C. albicans, its hyphae formation, adhesion and biofilm development. Extract prepared from S. boulardii culture filtrate was fractionated and GC-MS analysis showed that the active fraction contained, apart from 2-phenylethanol, caproic, caprylic and capric acid whose presence was confirmed by ESI-MS analysis. Biological activity was tested on C. albicans using extract and pure identified compounds. Our study demonstrated that this probiotic yeast secretes into the medium active compounds reducing candidal virulence factors. The chief compound inhibiting filamentous C. albicans growth comparably to S. boulardii extract was capric acid, which is thus responsible for inhibition of hyphae formation. It also reduced candidal adhesion and biofilm formation, though three times less than the extract, which thus contains other factors suppressing C. albicans adherence. The expression profile of selected genes associated with C. albicans virulence by real-time PCR showed a reduced expression of HWP1, INO1 and CSH1 genes in C. albicans cells treated with capric acid and S. boulardii extract. Hence capric acid secreted by S. boulardii is responsible for inhibition of C. albicans filamentation and partially also adhesion and biofilm formation.

The dimorphic fungus Candida albicans is a member of the normal flora residing in the intestinal tract of humans. In spite of this, under certain conditions it can induce both superficial and serious systemic diseases, as well as be the cause of gastrointestinal infections. Saccharomyces boulardii is a yeast strain that has been shown to have applications in the prevention and treatment of intestinal infections caused by bacterial pathogens. The purpose of this study was to determine whether S. boulardii affects the virulence factors of C. albicans. We demonstrate the inhibitory effect of live S. boulardii cells on the filamentation (hyphae and pseudohyphae formation) of C. albicans SC5314 strain proportional to the amount of S. boulardii added. An extract from S. boulardii culture has a similar effect. Live S. boulardii and the extract from S. boulardii culture filtrate diminish C. albicans adhesion to and subsequent biofilm formation on polystyrene surfaces under both aerobic and microaerophilic conditions. This effect is very strong and requires lower doses of S. boulardii cells or concentrations of the extract than serum-induced filamentation tests. Saccharomyces boulardii has a strong negative effect on very important virulence factors of C. albicans, i.e. the ability to form filaments and to adhere and form biofilms on plastic surfaces.