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At least 595 records · Page 33Linked to original sources
PubMed1983

Physiological control of repressible acid phosphatase gene transcripts in Saccharomyces cerevisiae.

We have examined the regulation of repressible acid phosphatase (APase; orthophosphoric-monoester phosphohydrolase [acid optimum], EC 3.1.3.2) in Saccharomyces cerevisiae at the physiological and molecular levels, through a series of repression and derepression experiments. We demonstrated that APase synthesis is tightly regulated throughout the growth phase and is influenced by exogenous and endogenous Pi pools. During growth in a nonlimiting Pi medium, APase is repressed. When external Pi becomes limiting, there is a biphasic appearance of APase mRNA and enzyme. Our data on APase mRNA half-lives and on the flux of intracellular Pi and polyphosphate during derepression are consistent with a mechanism of transcriptional autoregulation for the biphasic appearance of APase mRNA. Accordingly, preculture concentrations of Pi control the level of corepressor generated from intracellular polyphosphate degradation. When cells are fully derepressed, APase mRNA levels are constant, and the maximal linear accumulation rate of APase is observed. A scheme to integrate phosphorus metabolism and phosphatase regulation in S. cerevisiae is proposed.

Acid Phosphatase↗
PubMedDate not supplied

Differentiation of Rhizobium japonicum, I. enzymatic comparison of nitrogenase repressed and derepressed free living cells and of bacteroids.

Derepressed free living cells of Rhizobium japonicum strain 61-A-101 with leucine as single nitrogen source develop a maximum nitrogenase activity of 180 nmol C2H4.mg protein -1.H-1 in liquid culture under 2% 2% O2 in the gas phase. Only 10% of this activity is found with no oxygen in the gas phase during a 90 min incubation period. The maximum activity under 2% oxygen in the gas phase is unaffected by addition of 1-100 mM NH+4 and by addition of low concentrations of glutamine (0.36-1.44 mM). Specific activities of alanine dehydrogenase (E.C. 1.4.1.1.) asparatate aminotransferase (E.C. 2.6.1.1.) and, with much lower activities, of GOGAT (E.C. 1.4.1.13) in nitrogenase active free living cells are more similar to bacteroids than to nitrogenase repressed free living cells from liquid culture. The activities in nitrogenase repressed cells were about 50% lower. Glutamine synthetase (E.C. 6.3.1.2.) activity in bacteroids and in nitrogenase active cells were also similar, but only about 25-30% of that found in nitrogenase repressed Rhizobium japonicum cells.

Bacterial Proteins↗
PubMed1992

Chemically induced murine erythroleukemia cell differentiation is severely impaired when cAMP-dependent protein kinase activity is repressed by transfected genes.

During chemically induced differentiation of murine erythroleukemia (MEL) cells, cAMP-dependent protein kinase activity increases, and the enzyme's isozyme pattern changes. To examine the enzyme's role during MEL cell differentiation, we stably transfected MEL cells with recombinant plasmids in which the mouse metallothionein I promoter controlled expression of either a mutant form of the type I regulatory subunit of cAMP-dependent protein kinase (RI) or the enzyme's specific peptide inhibitor (PKI); expressing either sequence rendered cells cAMP-dependent protein kinase-deficient. Chemically induced differentiation of MEL cells as assessed by beta-globin mRNA and hemoglobin accumulation was inhibited in RI mutant and PKI transfectants; adding zinc further inhibited differentiation in the transfectants but had no effect on parental MEL cells. The inhibition of differentiation correlated with the amount of RI mutant mRNA and protein in the RI mutant transfectants and with the cells' degree of cAMP-dependent protein kinase deficiency in both the RI mutant and PKI transfectants. Overexpression of wild type RI did not interfere with differentiation or enzyme activity. We conclude that cAMP-dependent protein kinase activity is important for chemically induced differentiation of MEL cells and that the down-regulation of RI protein which occurs during MEL cell differentiation is not essential for differentiation to proceed.

Acetamides↗
PubMed2001

Non-repressing carbon sources for alcohol oxidase (AOX1) promoter of Pichia pastoris.

The growth of Pichia pastoris in a mixture of either glycerol or glucose and methanol follows a diauxic growth, with C1 utilizing enzymes being repressed. Therefore, these carbon sources can not be used as a mixture with methanol to simultaneously grow P. pastoris and induce C1 utilizing enzymes, especially in a shake flask cultures of AOX-deficient P. pastoris. Among the alternative carbon sources tested, alanine, sorbitol, mannitol and trehalose, did not repress beta-gal production when methanol was used as an inducer in mut- strain of P. pastoris. Our results show that either one of alanine, sorbitol, mannitol or trehalose can be used as a sole carbon and energy source for P. pastoris, although the doubling time on trehalose was very long. Mut- strains growing in media containing trehalose, alanine, sorbitol and mannitol with methanol (0.5%) as an inducing agent expressed as much or higher amount of beta-gal as compared to the mut+ growing in methanol containing media.

Journal Article↗