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Candida
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
Sexual reproduction is phenotypically controlled by the MAT gene located in the mating-type locus, for example, MAT locus in Saccharomyces cerevisiae. Two alleles of gene MAT—MATa and MATα—present in all cells, contain genetic information required for conjugation. Expression of conjugation type occurs by inserting the matching gene copy of MATa or MATα under promoter control at the MAT locus. Until recently, it was believed that the diploid yeasts Candida albicans cannot reproduce generatively. The discovery of the gene locus mating type-like (MTL) in the cells of Candida, which is equivalent to the MAT, became the basis for reexamining the potential for sexual reproduction in these yeasts. In vitro and in vivo studies have shown that there are two alleles MTL: MTLa and MTLα located on chromosome 5 in Candida albicans cells. Thus, strains can indeed be made to mate and form stable tetraploids.
Antifungal drug resistance: Significance and mechanisms
Published in Mahmoud A. Ghannoum, John R. Perfect, Antifungal Therapy, 2019
Sharvari Dharmaiah, Rania A. Sherif, Pranab K. Mukherjee
Transcriptional regulation of sterol biosynthesis genes plays a critical role in azole resistance and include zinc cluster proteins transcription factors (Zn2-Cys6 TFs) like TAC1 (transcriptional activator of CDR genes), MRR1/2 (multidrug resistance regulators that regulate MDR1), and UPC2 (activates the expression of related genes in response to sterol depletion through a conserved C-terminal domain) [152–162]. Recently, Hagiwara et al. [163] identified a novel Zn2-Cys6 Transcription Factor AtrR that co-regulates CYP51A and Cdr1B expression (by direct binding to both CYP51A and Cdr1B promoters) in A. fumigatus, A. oryzae, and A. nidulans, thus playing a critical role in azole resistance in these Aspegillus species. These investigators showed that while AtrR was responsible for the expression of CDR1B, SrbA was not involved in this process. Fluconazole-induced “microevolution” in C. albicans has also been suggested as a broader mechanism of resistance and comprises genomic rearrangements that result in gene amplification and loss of heterozygosity for resistance mutations (e.g., in mating type locus MTL), which further increases drug resistance and may also affect extended chromosomal regions with ancillary phenotypic effects [164]. For example, mutations in MTL allows the fungal cells to switch to the mating-competent opaque phenotype, allowing sexual recombination that may result in the generation of highly fluconazole-resistant strains with multiple resistance mechanisms.
Effect of low frequency magnetic field on efficiency of chromosome break repair
Published in Electromagnetic Biology and Medicine, 2020
Antonio M. Burgos-Molina, Silvia Mercado-Sáenz, Francisco Sendra-Portero, Miguel J. Ruiz-Gómez
S. cerevisiae strain AF2082 contains a 40 bp sequence from the mating type locus, MAT, including the cutting site for the HO endonuclease (HOcs), inserted into de URA3 gene on chromosome V. It also contains the gene encoding the HO endonuclease under control of a galactose-inducible promoter, inserted into the ADE3 locus. Upon growth of the cells in galactose-containing media, this endonuclease is expressed and introduces a staggered DSB at the HOcs. Because of the absence of a homologous donor sequence, this DSB has to be repaired by non-homologous end joining. Pho91 and Rmd5 derivatives of AF2082 contain a second DSB site generated by a pair of HOcs sequences flanking a selectable marker gene (TRP1) which confers tryptophane prototrophy. Successful cutting can thus be verified by loss of this marker gene and a tryptophane auxotrophic phenotype.