Substitution of histone H3 arginine 72 to alanine leads to the deregulation of isoleucine biosynthesis in the budding yeast Saccharomyces cerevisiae.

Histone residues play an essential role in the regulation of various biological processes. In the present study, we utilized the H3/H4 histone mutant library to probe the functional aspects of histone residues in amino acid biosynthesis. We found that the histone residue H3R72 plays a crucial role in the regulation of isoleucine biosynthesis. Substitution of the arginine residue (H3R72) of histone H3 to alanine (H3R72A) renders yeast cells unable to grow in minimal medium. Histone mutant H3R72A requires external supplementation of either isoleucine, serine, or threonine for growth in minimal medium. We also observed that the H3R72 residue and leucine amino acid in synthetic complete medium might play a crucial role in determining the intake of isoleucine and threonine in yeast. Furthermore, gene deletion analysis of ILV1 and CHA1 in the H3R72A mutant confirmed that isoleucine is the sole requirement for growth in minimal medium. Altogether, we have identified that histone H3R72 residue may be crucial for yeast growth in minimal medium by regulating isoleucine biosynthesis through the Ilv1 enzyme in the budding yeast Saccharomyces cerevisiae.

Identification of Histone H3 and H4 Amino Acid Residues Important for the Regulation of Arsenite Stress Signaling in Saccharomyces cerevisiae.

Arsenic is an environmental carcinogen that causes many diseases in humans, including cancers and organ failures, affecting millions of people in the world. Arsenic trioxide is a drug used for the treatment of acute promyelocytic leukemia (APL). In the present study, we screened the synthetic histone H3 and H4 library in the presence of arsenite to understand the role of histone residues in arsenic toxicity. We identified residues of histone H3 and H4 crucial for arsenite stress response. The residues H3T3, H3G90, H4K5, H4G13, and H4R95 are required for the activation of Hog1 kinase in response to arsenite exposure. We showed that a reduced level of Hog1 activation increases the intracellular arsenic content in these histone mutants through the Fps1 channel. We have also noticed the reduced expression of ACR3 exporter in the mutants. The growth defect of mutants caused by arsenite exposure was suppressed in hyperosmotic conditions, in a higher concentration of glucose, and upon deletion of the FPS1 gene. The arsenite sensitive histone mutants also showed a lack of H3K4 methylation and reduced H4K16 acetylation. Altogether, we have identified the key residues in histone H3 and H4 proteins important for the regulation of Hog1 signaling, Fps1 activity, and ACR3 expression during arsenite stress.

Zinc oxide nanoparticles induce toxicity by affecting cell wall integrity pathway, mitochondrial function and lipid homeostasis in Saccharomyces cerevisiae.

Growing numbers of nanotoxicity research demonstrating that mechanical damage and oxidative stress are potential modes of nanoparticles (NPs) induced toxicity. However, the underlying mechanisms by which NPs interact with the eukaryotic cell and affect their physiological and metabolic functions are not fully known. We investigated the toxic effects of zinc oxide nanoparticles (ZnO-NPs) on budding yeast, Saccharomyces cerevisiae and elucidated the underlying mechanism. We observed cell wall damage and accumulation of reactive oxygen species (ROS) leading to cell death upon ZnO-NPs exposure. We detected a significant change in the cellular distribution of lipid biosynthetic enzymes (Fas1 and Fas2). Furthermore, exposure of ZnO-NPs altered the architecture of endoplasmic reticulum (ER) and mitochondria as well as ER-mitochondria encounter structure (ERMES) complex causing cellular toxicity due to lipid disequilibrium and proteostasis. We also observed significant changes in heat shock and unfolded protein responses, monitored by Hsp104-GFP localization and cytosolic Hac1 splicing respectively. Moreover, we observed activation of MAP kinases of CWI (Mpk1) and HOG (Hog1) pathways upon exposure to ZnO-NPs. Transcript level analyses showed induction of chitin synthesis and redox homeostasis genes. Finally, we observed induction in lipid droplets (LDs) formation, distorted vacuolar morphology and induction of autophagy as monitored by localization of Atg8p. However, we did not observe any significant change in epigenetic marks, examined by western blotting. Altogether, we provide evidence that exposure of ZnO-NPs results in cell death by affecting cell wall integrity and ER homeostasis as well as accumulation of ROS and saturated free fatty acids.

A Pyridoindole-Based Multifunctional Bioprobe: pH-Induced Fluorescence Switching and Specific Targeting of Lipid Droplets.

A versatile fluorescent probe, PITE, based on alkyl-substituted pyridoindole (PI) and tetraphenylethylene (TE), which exhibits facile pH-induced fluorescence switching in solution, as nanoparticles, and in the solid state, is presented. Strong fluorescence in the solid state, as well as in solution and the aggregated state, allow sensing of toxic acid vapors. Fluorescence "off-on" switching of PITE through exposure to trifluoroacetic acid and triethylamine vapor is visualized by the naked eye. A unified picture of the switchable fluorescence of PITE is obtained by comprehensive spectroscopic investigations coupled with quantum mechanical calculations. Strong fluorescence, a large Stokes shift, high photostability, and biocompatibility of PITE make it a viable probe for subcellular imaging. Extensive fluorescence microscopic studies by employing organisms including lower and higher eukaryotes reveal specific localization of PITE to lipid droplets (LDs). LDs are dynamic subcellular organelles linked to various physiological processes and human diseases. Hence, the specific detection of LDs in diverse organisms is important to biomedical research and healthcare. Isolation of LDs and subsequent colocalization studies ascertain selective targeting of LDs by the easily affordable, lipophilic bioprobe, PITE. Thus, PITE is a promising multifunctional probe for chemosensing and the selective tracking of LDs.