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E Sakamoto

Publications and source records attributed to E Sakamoto.

At least 55 records · Page 3Linked to original sources
PubMed1987

Saccharomyces cerevisiae strains sensitive to inorganic mercury. III. Tyrosine uptake.

In Saccharomyces cerevisiae, the HGS2-1 allele confers sensitivities to inorganis mercury (Ono and Sakamoto 1985) and to excess fermentable sugars such as glucose (Sakamoto et al. 1985); exogenous tyrosine antagonizes both inorganic mercury and excess glucose. In this study, the inorganic mercury sensitive strain has been shown to have about twice more glucose-1,6-bisphosphate and slightly less pyruvate than the normal strains, suggesting that the inorganic mercury sensitive strain has the reduced aldolase activity. It has been also shown that the growth retarded cells accumulate trehalose, by which the lower level of glucose-6-phosphate in the inorganic mercury sensitive strain is accounted for, and that inorganic mercury, presumably excess glucose also, causes growth inhibition via depletion of cellular tyrosine. The mechanism how cellular tyrosine is depleted by inorganic mercury or excess glucose is accounted for by the facts that (1) the tyrosine uptake activity is decreased with increase of glucose concentration in growth medium, (2) HGS2-1 enhances the effect of glucose on the tyrosine uptake activity, and (3) inorganic mercury inhibits the tyrosine uptake system by binding to its SH-group(s). Thus, it is concluded that the role of tyrosine is not to detoxify inorganic mercury nor excess fermentable sugars but simply to counteract depletion of cellular tyrosine induced by them.

Biological Transport↗
PubMed1985

Saccharomyces cerevisiae strains sensitive to inorganic mercury. I. Effect of tyrosine.

From a cross of two strains of Saccharomyces cerevisiae, both of which had the same (wild type or normal) level of resistance to inorganic mercury, segregants having three distinguishable resistance levels, normal, sensitive and semi-sensitive, were obtained. Genetic analyses of the parents and the progeny indicated that the levels of inorganic mercury sensitivity were determined by three distinct loci, HGS1, HGS2 and MSM1. The recessive allele of the HGS1 locus, hgs1-1, and the codominant allele of the HGS2 locus, HGS2-1, were necessary for the sensitive phenotypes, and alleles in the MSM1 locus, MSM1-1 and msm1-2, were responsible for the different sensitivity levels. In short, the strains of genotypes hgs1-1 HGS2-1 msm1-2 and hgs1-1 HGS2-1 MSM1-1 were sensitive and semi-sensitive, respectively, while the strains of all other genotypes were normal. Although the hgs1-1 allele was identified as the aro7-1 mutation which confers deficiency of tyrosine and phenylalanine, mutations such as aro1B (deficiency of tyrosine, phenylalanine and tryptophan) and tyr1 (deficiency of tyrosine) had similar effects as aro7-1 on inorganic mercury sensitivity. From these results we conclude that the HGS2-1 allele causes inorganic mercury sensitivity when the cells are defective in the tyrosine biosynthesis. In fact, addition of tyrosine to the growth medium containing inorganic mercury resulted in increase of colony forming ability of the sensitive strains.

Culture Media↗
PubMed1985

Saccharomyces cerevisiae strains sensitive to inorganic mercury. II. Effect of glucose.

Saccharomyces cerevisiae strains sensitive to inorganic mercury (Ono and Sakamoto 1985) did not grow well on the medium rich in glucose and poor in peptone. This growth inhibition, like growth inhibition caused by inorganic mercury, was relieved by exogenous tyrosine. Sugars such as fructose and mannose were as inhibitory as glucose, but glycerol was not at all. Galactose was inhibitory but not so much as glucose. A gal2 mutation (defective in galactose uptake) partly relieved growth inhibition caused by excess galactose. Moreover, it was found that some of revertants which gained ability to grow well in the presence of excess glucose were defective in the glucose uptake. From these observations, we conclude that growth inhibition of the inorganic mercury sensitive strains by excess sugar is a consequence of the catabolite regulation. In other words, the inorganic mercury sensitive strains are hyper-sensitive to the catabolite regulation due to the presence of the HGS2-1 allele.

Culture Media↗