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Cadmium-resistant Saccharomyces cerevisiae strain 301N exhibits high basal as well as cadmium-induced expression of the CUP1 metallothionein gene. Since regulation of CUP1 is usually restricted to copper ions, our goal was to identify the factor responsible for the high metallothionein levels in strain 301N. The gene responsible for the observed phenotype is a spontaneously mutated heat shock transcription factor gene (HSF1). A double, semidominant HSF1 mutant with substitutions at codons 206 and 256 within the DNA-binding domain of the heat shock factor (HSF) confers two phenotypes. The first phenotype is elevated transcriptional activity of the HSF mutant (HSF301), which results in constitutive thermotolerance. A second HSF301 phenotype is enhanced binding affinity for the heat shock element (HSE) within the CUP1 5-sequences, resulting in high basal transcription of metallothionein. The CUP1 HSE is a minimal heat shock element containing only two perfectly spaced inverted repeats of the basic nGAAn block. Cells containing HSF301 are resistant to cadmium salts. The single R206S mutation is responsible for the high affinity binding to the CUP1 HSE. In addition, the R206S HSF substitution exhibits constitutive transcriptional activation from a consensus HSE (HSE2). The F256Y substitution in HSF attenuates the effects of R206S on the consensus HSE2, but not on the CUP1 HSE.All cells are capable of coping with changes in their environment, such as exposure to elevated temperatures, toxins, and oxidants. In response to certain stress conditions, activation of stress gene expression occurs, resulting in an elevated synthesis of stress proteins, commonly called heat shock proteins (hsp) 1 (1, 2). That these hsp genes are induced by a variety of stress conditions implies that they have broadly protective functions.The induction of heat shock protein(s) occurs at the level of transcription (3-5). Genes encoding the various hsp molecules contain a conserved promoter element, designated a heat shock element (HSE) (1, 6). The induction of hsp70 in animal cells by heat or metal ions requires only the HSE in the promoter (7,8). HSEs contain multiple 5-bp inverted repeats of the sequence nGAAn (9 -12). The number of 5-bp boxes may range from three to six (9 -11). A perfect consensus array of three boxes would be the sequence 5Ј-nGAAnnTTCnnGAAn-3Ј. Not all HSEs have perfect inverted repeats, but it appears that they have at least two perfect nGAAn boxes (9 -12). A compilation of 40 naturally occurring HSEs from different organisms revealed that seven contained only three nGAAn blocks, and in each case, these three nGAAn boxes were in combination with additional HSE units, permitting cooperative interactions (12).Transcriptional activation of genes containing heat shock promoter elements is mediated by the heat shock factor (HSF). Saccharomyces cerevisiae has one HSF encoded by the HSF1 locus (13,14). Yeast HSF is a trimeric protein reported to bind HSE sequences constitutively at low temperature (5,(15)(16)(17). Within the N-t...

The use of natural gas hydrate (NGH) as a natural gas transportation and storage medium is expected to meet further energy demand in the near future. To exploit NGH for industrial porposes, it is necessary to establish NGH storage systems using their self-preservation properties. In this report, NGH pellets containing CH 4 , C 2 H 6 , and C 3 H 8 were produced by continuous production using a bench-scale unit and successfully stored for 3 months at 253 K under atmospheric pressure. Qualitative and quantitative analyses [phase-contrast X-ray computed tomography (CT) by means of diffraction-enhanced imaging, cryogenic scanning electron microscopy, powder X-ray diffraction, and gas chromatography] were conducted to investigate the progression of dissociation. Some of the NGH pellets were also examined for their thermal history dependence between approximately 85 and 253 K after storage for 1 day or less to assess their stability under a rapid temperature change. The internal texture of the original NGH pellets was dense with hydrate even after 3 months of storage. On the other hand, thermal cracks covered with ice had formed in the hydrate pellet after the temperature rise (from 85 to 253 K). These cracks were assumed to be dissociation sites, but the dissociation was stopped only near the cracks. The mass fractions of NGH were larger than 70% after 3 months of storage and undergoing thermal history. These results demonstrate the excellent characteristics of NGH pellets produced by continuous production, improving their suitability for use as natural gas storage media.

This review describes nickel toxicity and nickel resistance mechanisms in fungi. Nickel toxicity in fungi is influenced by environmental factors such as pH, temperature and the existence of organic matter and other ions. We describe resistance mechanisms in nickel-resistant mutants of yeasts and filamentous fungi which were obtained by exposure to a mutagen or by successive culture in media containing increasing concentrations of nickel ion. Nickel resistance may involve: (1) inactivation of nickel toxicity by the production of extracellular nickel-chelating substances such as glutathione; (2) reduced nickel accumulation, probably by modification of a magnesium transport system; (3) sequestration of nickel into a vacuole associated with free histidine and involving Ni-insensitivity of vacuolar membrane H(+)-ATPase.

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