Eukaryotic organisms, like the model yeast S. cerevisiae, have linear chromosomes that facilitate organization and protection of nuclear DNA. A recent work described a stepwise break/repair method that enabled fusion of the 16 chromosomes of S. cerevisiae into a single large chromosome. Construction of this strain resulted in the removal of 30 of 32 telomeres, over 300 kb of subtelomeric DNA, and 107 subtelomeric ORFs. Despite these changes, characterization of the single chromosome strain uncovered modest phenotypes compared to a reference strain. This study further characterized the single chromosome strain and found that it exhibited a longer lag phase, increased doubling time, and lower final biomass concentration compared with a reference strain when grown on YPD. These phenotypes were amplified when ethanol was added to the medium or used as the sole carbon source. RNAseq analysis showed poor induction of genes involved in diauxic shift, ethanol metabolism, and fatty-acid ß-oxidation during growth on ethanol compared to the reference strain. Enzyme-constrained metabolic modeling identified decreased flux through the enzymes that are encoded by these poorly induced genes as a likely cause of diminished biomass accumulation. The diminished growth on ethanol for the single chromosome strain was rescued by nicotinamide, an inhibitor of sirtuin family deacetylases, which have been shown to silence gene expression in heterochromatic regions. Our results indicate that sirtuin-mediated silencing in the single chromosome strain interferes with growth on non-fermentable carbon sources. We propose that the removal of subtelomeric DNA that would otherwise be bound by sirtuins leads to silencing at other loci in the single chromosome strain. Further, we hypothesize that the poorly induced genes in the single chromosome strain during ethanol growth could be silenced by sirtuins in wildtype S. cerevisiae during growth on glucose.

中文翻译：

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酿酒酵母的单染色体菌株表现出乙醇代谢和耐受性降低


真核生物，如模型酵母酿酒酵母，具有促进核 DNA 组织和保护的线性染色体。最近的一项工作描述了一种逐步断裂/修复方法，该方法能够将酿酒酵母的 16 条染色体融合成一条大染色体。该菌株的构建导致去除了 32 个端粒中的 30 个、超过 300 kb 的亚端粒 DNA 和 107 个亚端粒 ORF。尽管有这些变化，与参考菌株相比，单染色体菌株的特征揭示了适度的表型。这项研究进一步表征了单染色体菌株，发现在 YPD 上生长时，与参考菌株相比，它表现出更长的滞后期、更长的倍增时间和更低的最终生物量浓度。当将乙醇添加到培养基中或用作唯一碳源时，这些表型被放大。 RNAseq 分析显示，与参考菌株相比，在乙醇中生长过程中，涉及双轴位移、乙醇代谢和脂肪酸 β-氧化的基因诱导较差。酶限制的代谢模型发现，这些诱导不良的基因编码的酶通量减少是生物量积累减少的可能原因。单染色体菌株在乙醇中的生长减弱可以通过烟酰胺来挽救，烟酰胺是sirtuin家族脱乙酰酶的抑制剂，已被证明可以沉默异染色质区域的基因表达。我们的结果表明，单染色体菌株中沉默调节蛋白介导的沉默会干扰在不可发酵碳源上的生长。我们提出，去除否则会被sirtuins结合的亚端粒DNA会导致单染色体菌株中其他基因座的沉默。 此外，我们假设在乙醇生长过程中单染色体菌株中诱导不良的基因可以在野生型酿酒酵母中在葡萄糖生长过程中被去乙酰化酶沉默。