Xylene causes oxidative stress and pronounced translation repression in Saccharomyces cerevisiae.

Organic solvent-resistant microorganisms are strongly desired for efficient fermentative production of hydrophobic substances in water-organic solvent two-phase systems. To improve organic solvent-resistance of microorganisms, a better understanding of the effects of organic solvents on microbial cells and cellular responses to organic solvents is essential. So far, various bacteria have been studied for their response mechanisms against organic solvents and improvement of their resistance to organic solvents. On the other hand, limited information is available on the effects of organic solvents on eukaryotic microorganisms. We herein examined the physiological effects of xylene, one of representative organic solvents, on the budding yeast Saccharomyces cerevisiae. We found that xylene induced fragmentation of mitochondria and the nuclear accumulation of Yap1, an oxidative stress responsive transcription factor, followed by the transcriptional activation of its target genes, GPX2 and TRX2, in yeast cells treated with xylene. These findings indicate that xylene caused oxidative stress in yeast cells. However, treatment with 0.03% (v/v) or more of xylene severely repressed the translation activity of yeast cells. Therefore, the expected protein synthesis of Yap1-target genes was not observed despite the transcriptional activation in cells treated with 0.03% (v/v) xylene. This is the first report on the inhibitory effects of xylene on bulk translation activity and provides novel insights into the toxicity of xylene.

The Histone Deacetylase Gene Rpd3 Is Required for Starvation Stress Resistance.

Epigenetic regulation in starvation is important but not fully understood yet. Here we identified the Rpd3 gene, a Drosophila homolog of histone deacetylase 1, as a critical epigenetic regulator for acquiring starvation stress resistance. Immunostaining analyses of Drosophila fat body revealed that the subcellular localization and levels of Rpd3 dynamically changed responding to starvation stress. In response to starvation stress, the level of Rpd3 rapidly increased, and it accumulated in the nucleolus in what appeared to be foci. These observations suggest that Rpd3 plays a role in regulation of rRNA synthesis in the nucleolus. The RT-qPCR and ChIP-qPCR analyses clarified that Rpd3 binds to the genomic region containing the rRNA promoters and activates rRNA synthesis in response to starvation stress. Polysome analyses revealed that the amount of polysomes was decreased in Rpd3 knockdown flies under starvation stress compared with the control flies. Since the autophagy-related proteins are known to be starvation stress tolerance proteins, we examined autophagy activity, and it was reduced in Rpd3 knockdown flies. Taken together, we conclude that Rpd3 accumulates in the nucleolus in the early stage of starvation, upregulates rRNA synthesis, maintains the polysome amount for translation, and finally increases stress tolerance proteins, such as autophagy-related proteins, to acquire starvation stress resistance.