Positive and negative regulation of a sterol biosynthetic gene (ERG3) in the post-squalene portion of the yeast ergosterol pathway

AbstractRegulation of sterol biosynthesis in the terminal portion of the pathway represents an efficient mechanism by which the cell can control the production of sterol without disturbing the production of other essential mevalonate pathway products. We demonstrate that mutations affecting early and late steps in sterol homeostasis modulate the expression of the ERG3 gene: a late step in sterol biosynthesis in yeast. Expression of ERG3 is increased in response to a mutation in the major isoform of HMG CoA reductase which catalyzes the rate-limiting step of sterol biosynthesis. Likewise, mutations in non-auxotrophic ergosterol biosynthetic genes downstream of squalene production (erg2, erg3, erg4, erg5, and erg6) result in an up-regulation of ERG3 expression. Deletion analysis of the ERG3 promoter identified two upstream activation sequences: UAS1, which when deleted reduces ERG3 gene expression 3–4-fold but maintains sterol regulation and UAS2, which when deleted further reduces ERG3 expression and abolishes sterol regulation. The recent isolation of two yeast genes responsible for the esterification of intracellular sterol (ARE1 and ARE2) has enabled us to directly analyze the relationship between sterol esterification and de novo biosynthesis. Our results demonstrate that the absence of sterol esterification leads to a decrease in total intracellular sterol and ERG3 is a target of this negative regulation

Environmental straits of Cryptococcus neoformans variety grubii in the city of Santos, SP, Brazil Amostras ambientais de Cryptococcus neoformans var. grubii na cidade de Santos, SP, Brasil

This study involved a total of 116 samples, 79 taken from pigeon droppings and 37 of atmospheric air taken close to accumulations of excrement. Cryptococcus neoformans var. grubii was isolated from 11 (13.9%) of these samples. Other species of Cryptococcus were also isolated from these samples, such as C. albidus (12.6%) and C. laurentii (8.9%). C. neoformans was not isolated from the air samples, though C. albidus (5.4%) was. All the strains of C. neoformans were found to belong to the A serotype (C. neoformans var. grubii). In regard to the studies with the antifungal agents 5-fluorocytosine, fluconazole, itraconazole, amphotericin B and voriconazole, by means of the microdilution method (EUCAST), we point out that one sample demonstrated resistance to fluconazole, this being especially significant because this is an environmental strain.<br>Analisaram-se 116 amostras, sendo 79 de fezes de pombos e 37 de ar atmosférico de regiões com acúmulo de fezes. Isolou-se Cryptococcus neoformans var. neoformans de 11 (13.9%) destas amostras. Outras espécies de Cryptococcus também foram isoladas destas amostras tais como C. laurentii (8.9%) e C. albidus (12.6 %), o qual também foi isolado de amostras do ar (5.4 %). Todas as amostras de C. neoformans foram sorotipo A (C. neoformans var. grubii). Em relação à avaliação do perfil de sensibilidade às drogas antifúngicas (5-fluorocitosina, fluconazol, itraconazol, anfotericina B e voriconazol) pelo método da microdiluição (EUCAST, 2002), destacou-se a presença de uma amostra com valor de concentração inibitória mínima (CIM) elevado para fluconazol, sendo de grande significância, uma vez tratar-se de isolado ambiental