Saccharomyces cerevisiae sake yeast strain Kyokai no. 7 (K7) and its relatives carry a homozygous loss-of-function mutation in the RIM15 gene, which encodes a Greatwall family protein kinase. Disruption of RIM15 in nonsake yeast strains leads to improved alcoholic fermentation, indicating that the defect in Rim15p is associated with the enhanced fermentation performance of sake yeast cells. In order to understand how Rim15p mediates fermentation control, we here focused on target-of-rapamycin protein kinase complex 1 (TORC1) and protein phosphatase 2A with the B55δ regulatory subunit (PP2AB55δ), complexes that are known to act upstream and downstream of Rim15p, respectively. Several lines of evidence, including our previous transcriptomic analysis data, suggested enhanced TORC1 signaling in sake yeast cells during sake fermentation. Fermentation tests of the TORC1-related mutants using a laboratory strain revealed that TORC1 signaling positively regulates the initial fermentation rate in a Rim15p-dependent manner. Deletion of the CDC55 gene, encoding B55δ, abolished the high fermentation performance of Rim15p-deficient laboratory yeast and sake yeast cells, indicating that PP2AB55δ mediates the fermentation control by TORC1 and Rim15p. The TORC1-Greatwall-PP2AB55δ pathway similarly affected the fermentation rate in the fission yeast Schizosaccharomyces pombe, strongly suggesting that the evolutionarily conserved pathway governs alcoholic fermentation in yeasts. It is likely that elevated PP2AB55δ activity accounts for the high fermentation performance of sake yeast cells. Heterozygous loss-of-function mutations in CDC55 found in K7-related sake strains may indicate that the Rim15p-deficient phenotypes are disadvantageous to cell survival. IMPORTANCE The biochemical processes and enzymes responsible for glycolysis and alcoholic fermentation by the yeast S. cerevisiae have long been the subject of scientific research. Nevertheless, the factors determining fermentation performance in vivo are not fully understood. As a result, the industrial breeding of yeast strains has required empirical characterization of fermentation by screening numerous mutants through laborious fermentation tests. To establish a rational and efficient breeding strategy, key regulators of alcoholic fermentation need to be identified. In the present study, we focused on how sake yeast strains of S. cerevisiae have acquired high alcoholic fermentation performance. Our findings provide a rational molecular basis to design yeast strains with optimal fermentation performance for production of alcoholic beverages and bioethanol. In addition, as the evolutionarily conserved TORC1-Greatwall-PP2AB55δ pathway plays a major role in the glycolytic control, our work may contribute to research on carbohydrate metabolism in higher eukaryotes.

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The potential contamination with radionuclides released by the Fukushima Daiichi Nuclear Power Plant Accident following the great east Japan earthquake and tsunami in March 2011 of agricultural products and processed foods derived from them is a matter of on-going concern. The stable 133 Cs is a useful indicator for predicting the behaviour of radioactive Cs, and potassium (K) is a congener of Cs. In this study, the distribution of 133 Cs and K in Ume fruit, and the transfer of 133 Cs and K from Ume fruit to Ume liqueur, were investigated. The concentrations of 133 Cs and K in Ume fruit were highest in the skin, followed by the kernel or flesh, and then the pit. About 80% of 133 Cs and K in all Ume fruits was distributed in the flesh. The transfer ratios of 133 Cs and K from Ume fruit to Ume liqueur were similar among all cultivars after 3 months, and they were similar to those of organic acids. The food retention factor (Fr = weight of 133 Cs in Ume liqueur/weight of 133 Cs in Ume fruit) was ca. 0.8, and the processing factor (Pf = concentration of 133 Cs in Ume liqueur/concentration of 133 Cs in Ume fruit) was 0.2-0.3. From the present study, the radioactivity of Ume liqueur would be below the legal limit if made using Ume fruits within the legal limit, thereby confirming the safety of Ume liqueur.

27Sake yeast strain Kyokai no. 7 (K7) and its Saccharomyces cerevisiae relatives carry a 28 homozygous loss-of-function mutation in the RIM15 gene, which encodes a 29Greatwall-family protein kinase. Disruption of RIM15 in non-sake yeast strains leads to 30 addition, as the evolutionarily conserved TORC1-Greatwall-PP2A B55δ pathway plays a 61 major role in the glycolytic control, our work may contribute to research on carbohydrate 62 metabolism in higher eukaryotes. 63 64