| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1998: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Candida tropicalis is an asporogenic diploid yeast which is characterized by its ability to utilize n-alkanes as a sole carbon and energy source. In assimilating n-alkanes, C.tropicalis shows a change in its intracellular structure by proliferating a large number of peroxisomes. Peroxisomes are versatile, single-membrane-bound organelles occurring in most of eukaryotic cells. Concomitant with peroxisome proliferation, the activities of peroxisomal enzymes are induced in n-alkane-grown cells. On the other hand, they are synthesized at low rate or not at all in glucose-grown cells. This phenomenon is called as glucose repression. Isociterate lyase (ICL), a key enzyme of the glyoxylate cycle being localized in peroxisomes, is under the control of glucose repression. Promoters of Saccharomyces cerevisiae controlled by the glucose repression mechanism were used to search for cis-regulatory elements responsible for derepression of gene expression. Various trans-acting factors which are invol
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ved in the genetic regulation of the glucose repression in S.cerevisiae, were also identified. The fact that UPR-ICL-mediated transcription of C.tropicalis is still glucose-repressive in S.cerevisiae demonstrates that similar mechanisms are commonly existing in both of the yeast strains concerning the regulation of ICL gene. A mutant was isolated that failed to derepress the UPR-ICL-mediated gene expression in acetate medium, and the gene (FILl) that complemented this mutation was isolated. The fill null mutant in which FILl is disrupted could not grow on acetate or ethanol, and the derepression of the isocitrate lyase encoded by ICLl in S.cerevisiae was also defected. The amino acid sequence of Fillp (230 amino acids) showed similarity to ribosome recycling factors (RRFs) of prokaryotes. Compared to prokaryotic RRFs, Fil ip had an N-terminal 46 amino acid extension which was shown to be able to function as a mitochondrial targeting sequence. The subcellular fractionation of the DELTAfil 1 strain showed that protein constituents of the mitochondrial fraction of the DELTAfil 1 strain differed from those of the wild type strain, but resembled those of chloramphenicol-treated cells or rho。 cells. These results suggest that Fillp is necessary for protein synthesis in mitochondria of S.cerevisiae. The results indicate the presence of a communication pathway between mitochondria and the nucleus which represses expression of genes encoding the key enzymes of the glyoxylate cycle and gluconeogenic pathway when there is a deficiency in the mitochondrial respiratory chain. Less
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