Transcription factors Atf1 and Sty1 promote stress tolerance under nitrosative stress in Schizosaccharomyces pombe.

Nitric Oxide (NO) and its associated reactive nitrogen species (RNS) produce nitrosative stress under various pathophysiological conditions in eukaryotes. The fission yeast Schizosaccharomyces pombe regulates stress response mainly through the Sty1-Atf1 MAP Kinase pathway. The present study deals with the role of transcription factor Atf1 and Sty1 in S. pombe under nitrosative stress. In this study, exposure to an NO donor resulted in S-phase slowdown with associated mitotic block in S. pombe. Deletion of sty1 and atf1 in S. pombe had differential growth sensitivity towards NO donor. Both Sty1 and Atf1 were involved in regulating mitotic slowdown in S. pombe under nitrosative stress. Experimental data obtained in this study reveals a novel role of Atf1 in initiating the replication slowdown in S. pombe under nitrosative stress. Both Sty1 and Atf1 were accumulated in the nucleus in S. pombe under nitrosative stress in a concentration and time dependent manner. Atf1 is also found to be nuclear delocalized under longer nitrosative stress.

Nitric oxide sensing by chlorophyll a.

Nitric oxide (NO) acts as a signalling molecule that has direct and indirect regulatory roles in various functional processes in biology, though in plant kingdom its role is relatively unexplored. One reason for this is the fact that sensing of NO is always challenging. There are very few probes that can classify the different NO species. The present paper proposes a simple but straightforward way for sensing different NO species using chlorophyll, the source of inspiration being hemoglobin that serves as NO sink in mammalian systems. The proposed method is able to classify NO from DETA-NONOate or (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1,2-diolate, nitrite, nitrate and S-nitrosothiol or SNO. This discrimination is carried out by chlorophyll a (chl a) at nano molar (nM) order of sensitivity and at 293 K-310 K. Molecular docking reveals the differential binding effects of NO and SNO with chlorophyll, the predicted binding affinity matching with the experimental observation. Additional experiments with a diverse range of cyanobacteria reveal that apart from the spectroscopic approach the proposed sensing module can be used in microscopic inspection of NO species. Binding of NO is sensitive to temperature and static magnetic field. This provides additional support for the involvement of the porphyrin ring structures to the NO sensing process. This also, broadens the scope of the sensing methods as hinted in the text.

Multimodal control of transcription factor Pap1 in Schizosaccharomyces pombe under nitrosative stress.

Schizosaccharomyces pombe Pap1, a bZIP transcription factor, is highly homologous to the mammalian c-Jun protein that belongs to the AP1 family of transcriptional regulators. The role of transcription factor Pap1 has been extensively studied under oxidative stress. Two cysteine residues in Pap1p namely, C278 and C501 form disulfide linkage under oxidative stress resulting in nuclear accumulation. We first time showed the involvement of Pap1 in the protection against nitrosative stress. In the present study we show that pap1 deletion makes growth of S. pombe sensitive to nitrosative stress. pap1 deletion also causes delayed recovery in terms of mitotic index under nitrosative stress. Our flow cytometry data shows that pap1 deletion causes slower recovery from the slowdown of DNA replication under nitrosative stress. This is the first report where we show that Pap1 transcription factor is localized in the nucleus under nitrosative stress. From our study it is evident that nuclear localization of Pap1 under nitrosative stress was not due to reactive oxygen species formation.

Nitrosative stress induces a novel intra-S checkpoint pathway in Schizosaccharomyces pombe involving phosphorylation of Cdc2 by Wee1.

Excess production of nitric oxide and reactive nitrogen intermediates causes nitrosative stress on cells. Schizosaccharomyces pombe was used as a model to study the cell cycle regulation under nitrosative stress response. We discovered a novel intra-S-phase checkpoint that is activated in S. pombe under nitrosative stress. The mechanism for this intra-S-phase checkpoint activation is distinctly different than previously reported for genotoxic stress in S. pombe by methyl methane sulfonate. Our flow cytometry data established the fact that Wee1 phosphorylates Cdc2 Tyr15 which leads to replication slowdown in the fission yeast under nitrosative stress. We checked the roles of Rad3, Rad17, Rad26, Swi1, Swi3, Cds1, and Chk1 under nitrosative stress but those were not involved in the activation of the DNA replication checkpoint. Rad24 was found to be involved in intra-S-phase checkpoint activation in S. pombe under nitrosative stress but that was independent of Cdc25.