Mating reaction in Saccharomyces cerevisiae. IX. Regulation of sexual cell agglutinability of a type cells by a sex factor produced by alpha type cells

Preventability and manageability of adverse drug reactions in COVID-19 with mucormycosis: An observational study

Background

In the intricate landscape of healthcare amid the COVID-19 pandemic, the emergence of mucormycosis as a severe complication posed a significant challenge to primary healthcare. This study delved into the complexities of adverse drug reactions (ADRs) in COVID-19 patients with mucormycosis undergoing treatment with conventional amphotericin B.

Methods

Ethically approved and meticulously conducted, the study scrutinized 154 ADRs in depth, shedding light on their classification, outcomes, and interventions in COVID patients with mucormycosis. A descriptive analysis was carried out to report the findings of this study.

Results

The findings revealed that a substantial proportion (85.6%) of these ADRs were manageable, emphasizing the need for vigilant monitoring and timely interventions. Notably, gender disparities surfaced, indicating potential gender-specific responses to amphotericin B. Causality assessments based on the WHO-UMC scale classified the majority of ADRs as certain, providing a robust foundation for understanding the intricate relationships between amphotericin B and the observed adverse events.

Conclusion

This research not only categorizes ADRs as preventable and manageable but also offers practical insights into their nature and the diverse strategies employed for their management. The study's outcomes underline the importance of personalized healthcare approaches that can be adopted by primary care physicians for effective patient care.

Sexual agglutination in budding yeasts: structure, function, and regulation of adhesion glycoproteins

The sexual agglutinins of the budding yeasts are cell adhesion proteins that promote aggregation of cells during mating. In each yeast species, complementary agglutinins are expressed by cells of opposite mating type that interact to mediate aggregation. Saccharomyces cerevisiae alpha-agglutinin and its analogs from other yeasts are single-subunit glycoproteins that contain N-linked and O-linked oligosaccharides. The N-glycosidase-sensitive carbohydrate is not necessary for activity. The proposed binding domain of alpha-agglutinin has features characteristic of the immunoglobulin fold structures of cell adhesion proteins of higher eukaryotes. The C-terminal region of alpha-agglutinin plays a role in anchoring the glycoprotein to the cell surface. The S. cerevisiae alpha-agglutinin and its analogs from other species contain multiple subunits; one or more binding subunits, which interact with the opposite agglutinin, are disulfide bonded to a core subunit, which mediates cell wall anchorage. The core subunits are composed of 80 to 95% O-linked carbohydrate. The binding subunits have less carbohydrate, and both carbohydrate and peptide play roles in binding. The alpha-agglutinin and alpha-agglutinin genes from S. cerevisiae have been cloned and shown to be regulated by the mating-type locus, MAT, and by pheromone induction. The agglutinins are necessary for mating under conditions that do not promote cell-cell contact. The role of the agglutinins therefore is to promote close interactions between cells of opposite mating type and possibly to facilitate the response to phermone, thus increasing the efficiency of mating. We speculate that they mediate enhanced response to sex pheromones by providing a synapse at the point of cell-cell contact, at which both pheromone secretion and cell fusion occur.

Pheromonal regulation and sequence of the Saccharomyces cerevisiae SST2 gene: a model for desensitization to pheromone

Strains of both haploid mating types containing sst2 mutations are altered in response to pheromone; MATa sst2 cells are supersensitive to alpha-factor, and MAT alpha sst2 cells are supersensitive to a-factor. This phenotype suggests that SST2 encodes a component of the pheromone response pathway that is common to both mating types. We have cloned the SST2 gene by isolation of multicopy plasmids that complement the sst2-1 mutation. One such plasmid contained a 4.5-kilobase HindIII fragment that was able to complement the sst2-1 mutation in high or low copy number, integrated at the SST2 locus, and resulted in an sst2 phenotype when disrupted, indicating that this fragment contained the SST2 gene. We identified the functional region of the complementing DNA fragment by transposon mutagenesis. Sequencing of this fragment identified an open reading frame encoding 698 amino acids at a position that correlated well with the functional region. Expression of an Sst2-beta-galactosidase fusion was haploid specific and induced by exposure to pheromone. We discuss a model in which induction of the SST2 product results in inhibition of a component of the pheromone response pathway, resulting in desensitization to pheromone.

Pheromonal regulation and sequence of the Saccharomyces cerevisiae SST2 gene: a model for desensitization to pheromone

Strains of both haploid mating types containing sst2 mutations are altered in response to pheromone; MATa sst2 cells are supersensitive to alpha-factor, and MAT alpha sst2 cells are supersensitive to a-factor. This phenotype suggests that SST2 encodes a component of the pheromone response pathway that is common to both mating types. We have cloned the SST2 gene by isolation of multicopy plasmids that complement the sst2-1 mutation. One such plasmid contained a 4.5-kilobase HindIII fragment that was able to complement the sst2-1 mutation in high or low copy number, integrated at the SST2 locus, and resulted in an sst2 phenotype when disrupted, indicating that this fragment contained the SST2 gene. We identified the functional region of the complementing DNA fragment by transposon mutagenesis. Sequencing of this fragment identified an open reading frame encoding 698 amino acids at a position that correlated well with the functional region. Expression of an Sst2-beta-galactosidase fusion was haploid specific and induced by exposure to pheromone. We discuss a model in which induction of the SST2 product results in inhibition of a component of the pheromone response pathway, resulting in desensitization to pheromone.

Pheromone induction of agglutination in Saccharomyces cerevisiae a cells

a-Agglutinin, the cell surface sexual agglutinin of yeast a cells, was assayed by its ability to bind its complementary agglutinin, alpha-agglutinin. The specific binding of 125I-alpha-agglutinin to a cells treated with the sex pheromone alpha-factor was 2 to 2.5 times that of binding to a cells not treated with alpha-factor. Competition with unlabeled alpha-agglutinin revealed that the increased binding was due to increased cell surface expression of a-agglutinin, with no apparent change in the binding constant. The increase in site number was similar to the increase in cellular agglutinability. Increased expression of a-agglutinin followed the same kinetics as the increase in cellular agglutinability, with a 10-min lag followed by a 15- to 20-min response time. Induction kinetics were similar in cells in phases G1 and G2 of the cell cycle. Maximal expression levels were similar in cells treated with excess pheromone and in cells exposed to pheromone after destruction of constitutively expressed a-agglutinin.

Alpha mating type-specific expression of mutations leading to constitutive agglutinability in Saccharomyces cerevisiae

Two mutants of Saccharomyces cerevisiae have been isolated and characterized. The mutants were constitutively agglutinable at 36 degrees C, the temperature at which wild-type cells agglutinate only after induction by mating pheromone. The mutant cells had other properties specific for the normal alpha cell type, i.e., conjugation with a cells, response to a mating pheromone, and production of alpha mating pheromone. The two mutations, cag1 and cag2, were recessive and expressed only in alpha cells. cag1 is linked very closely to the MAT locus, but cag2 is unlinked to the MAT locus. These cag mutations complemented ste3-1. These results indicate that CAG genes are novel alpha-specific genes involved in the regulation of sex agglutinin synthesis.

Physiological characterization of Saccharomyces cerevisiae mutants supersensitive to G1 arrest by a factor and alpha factor pheromones

Saccharomyces cerevisiae MATa cells carrying mutations in either sst1 or sst2 are supersensitive to the G1 arrest induced by alpha factor pheromone. When sst1 mutants were mixed with normal SST+ cells, the entire population recovered together from alpha factor arrest, suggesting that SST+ cells helped sst1 mutants to recover. Complementation tests and linkage analysis showed that sst1 and bar1, a mutation which eliminates the ability of MATa cells to act as a "barrier" to the diffusion of alpha factor, were lesions in the same genes. These findings suggest that sst1 mutants, are defective in recovery from alpha factor arrest because they are unable to degrade the pheromone. In contrast, recovery of sst2 mutants was not potentiated by the presence of SST+ cells in mixing experiments. When either normal MATa cells or mutant cells carrying defects in sst1 or sst2 were exposed to alpha factor for 1 h and then washed free of the pheromone, the sst2 cells subsequently remained arrested in the absence of alpha factor for a much longer time than SST+ or sst1 cells. These observations suggest that the defect in sst2 mutants is intrinsic to the cell and is involved in the mechanism of alpha factor action at some step after the initial interaction of the pheromone with the cell. The presence of an sst2 mutation appears to cause a growth debility, since repeated serial subculture of haploid sst2-1 strains led to the accumulation of faster-growing revertants that were pheromone resistant and were mating defective ("sterile").

Physiological characterization of Saccharomyces cerevisiae mutants supersensitive to G1 arrest by a factor and alpha factor pheromones

Saccharomyces cerevisiae MATa cells carrying mutations in either sst1 or sst2 are supersensitive to the G1 arrest induced by alpha factor pheromone. When sst1 mutants were mixed with normal SST+ cells, the entire population recovered together from alpha factor arrest, suggesting that SST+ cells helped sst1 mutants to recover. Complementation tests and linkage analysis showed that sst1 and bar1, a mutation which eliminates the ability of MATa cells to act as a "barrier" to the diffusion of alpha factor, were lesions in the same genes. These findings suggest that sst1 mutants, are defective in recovery from alpha factor arrest because they are unable to degrade the pheromone. In contrast, recovery of sst2 mutants was not potentiated by the presence of SST+ cells in mixing experiments. When either normal MATa cells or mutant cells carrying defects in sst1 or sst2 were exposed to alpha factor for 1 h and then washed free of the pheromone, the sst2 cells subsequently remained arrested in the absence of alpha factor for a much longer time than SST+ or sst1 cells. These observations suggest that the defect in sst2 mutants is intrinsic to the cell and is involved in the mechanism of alpha factor action at some step after the initial interaction of the pheromone with the cell. The presence of an sst2 mutation appears to cause a growth debility, since repeated serial subculture of haploid sst2-1 strains led to the accumulation of faster-growing revertants that were pheromone resistant and were mating defective ("sterile").

Cell-cell recognition in Saccharomyces cerevisiae: regulation of mating-specific adhesion

Mating-specific adhesion between haploid yeast cells of opposite mating type (a and alpha) was studied by using a quantitative agar plate assay. Washed a and alpha cells that had not previously been exposed to their respective opposite mating type ("naive" cells) adhered relatively weakly. In water, only 5 to 10% of the a cells stuck tightly enough to alpha cells to give rise subsequently to diploid clones on the assay plates. Under optimum conditions (pH 6 to 7, at least 0.1 M Nacl or 0.01 M Mg(2+)), there was about 20% adhesion. Nevertheless, this weak binding defined a mating type-specific interaction because, even under optimum conditions, the homologous interactions (a with a and alpha with alpha) yielded only 3 to 5% cohesion. In contrast to these results, washed cells that had been preincubated in the cell-free culture medium of their opposite mating type ("preconditioned" cells) adhered quite strongly. The degree of adhesion between preconditioned cells (40 to 50%) was essentially unaffected by extremes of ionic strength, pH, and temperature and by the absence of divalent cation. This strong interaction was also mating type specific since cohesion between preconditioned cells of like mating type was only about 5%. The increase in agglutinability was obtained if only the a cells were preconditioned and could be induced by highly purified preparations of natural or synthetically prepared alpha-factor, an oligopeptide pheromone released by the alpha cells. The appearance of increased adhesiveness was blocked by an inhibitor of RNA synthesis and by an inhibitor of protein synthesis, but not by an inhibitor of polysaccharide synthesis. Adhesion between preconditioned cells could be inhibited by pretreatment with functionally univalent succinylated concanavalin A or with extracts from preconditioned cells of the opposite mating type. These results confirm in a quantitative manner that the recognition between conjugating cells of S. cerevisiae is a developmentally regulated event that is under the control of the mating type locus.

Mating reaction in Saccharomyces cerevisiae. X. Agglutinability-inactivating factor: a factor which destroys sexual agglutinability of a mating-type cells

From cells of Saccharomyces cerevisiae a factor has been extracted that destroys the agglutinability of a mating-type cells specifically. It was found in the cell extracts of diploid and tetraploid strains as well as haploid strains of a and alpha mating types. It is heat-labile and the molecular weight is about 50,000. It is adsorbed by neither a cells nor alpha cells. Its biological activity is dependent on the incubation temperature and the pH, and is completely inhibited by phenylmethylsulfonyl fluoride, a potent inhibitor of the serine proteases. All the results described in this paper indicate that this factor is a proteolytic enzyme.