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At least 847 records · Page 47Linked to original sources
PubMed2006

HPV16E7 mediates HADC chromatin repression and downregulation of MHC class I genes in HPV16 tumorigenic cells through interaction with an MHC class I promoter.

Downregulation of the expression of major histocompatibility complex class I antigens on the surface of high-risk HPVs-transformed cells may contribute to their high tumorigenic potential, which enables them to escape immune recognition by cytotoxic T lymphocytes. In this study, we show that the viral E7 oncoprotein mediates transcriptional downregulation of the major histocompatibility complex (MHC) class I genes by targeting the class I promoter in HPV16 containing CaSki tumor cells. Using the chromatin immunoprecipitation assay, we demonstrated that HPV16E7 and specific HADCs, including HADC1, HADC2, and HADC8, are physically associated with the class I promoter and the histone of the class I promoter was deacetylated. Knocking down of HPV16E7 expression with the E7-specific small interfering RNA induced the release of HPV17E7 as well as HDAC1 and HDAC2 from the class I promoter. Furthermore, HPV16E7 siRNA resulted in a dramatic increase in histone acetylation. Importantly, MHC class I antigen expression was up-regulated on the surface of cells transfected with the E7 siRNA, but not on that of untransfected cells. Taken together, our results demonstrate that the HPV16E7 protein is associated with the MHC class I promoter and mediates MHC class I downregulation by repressing chromatin activation.

Cell Line, Tumor↗
PubMed1975

Catabolite repression of Pseudomonas aeruginosa amidase: isolation of promotor mutants.

Among mutants of Pseudomonas aeruginosa isolated from fluoroacetamide medium were some which synthesized amidase at about 5% of the rate of the parent constitutive strain, PAC101. Seven fluoroacetamide-resistant mutants with low amidase activity gave rise to secondary mutant strains on succinate+butyramide plates. One appeared to be an 'up-promotor' mutant and synthesized amidase at a high rate. This mutant, PAC433, was not stimulated by cyclic-AMP and was much less sensitive to catabolite repression by succinate. The mutation conferring resistance to catabolite repression was cotransduced at a frequency of 96% (26/27) with the amidase genes amiR, amiE. Five other revertants had catabolite repression-resistance mutations which were linked to the amidase genes and these also were probably promotor mutants. One strain had a mutation conferring resistance to catabolite repression which was unlinked to the amidase genes.

Acetamides↗
PubMed1976

Mutations in Escherichia coli that relieve catabolite repression of tryptophanase synthesis. Mutations distant from the tryptophanase gene.

Two mutants are described in which the synthesis of tryptophanase is unusually insensitive to catabolite repression. Neither mutation is linked by transduction to the tryptophane structural gene, neither mutation renders the synthesis of beta-galactosidase insensitive to catabolite repression, and the mutations do not permit tryptophanase to be synthesized in strains deficient in adenyl cyclase. During growth in glucose-minimal medium the mutants maintained a similar intracellular concentration of cyclic AMP to their wild-type parent; but since in the wild type the concentration of cyclic AMP was the same in glycerol-minimal medium as in glucose-minimal medium, it is doubtful whether catabolite repression is mediated by measurable changes in the concentration of this nucleotide.

Adenylyl Cyclases↗
PubMed2002

Construction of alpha-amylase-producing strains not subject to carbon catabolite repression.

The dyatic symmetric element (DSE) present in the alpha-amylase gene promoter region of the thermophilic Streptomyces strain sp. TO1, and the whole alpha-amylase gene (amy TO1) with a 3-bp change in the DSE, were cloned in the high copy number replicative cloning vector pIJ702 giving pLM10 and pLM11 plasmids respectively. In TO1/pLM10 and Streptomyces lividans TK24/pLM11 strains, the expression of alpha-amylase TO1 gene became insensible to the negative effect of glucose and glycerol. These results strongly suggest that, in a high copy number system, the negative transcriptional regulator was titrated out by the DSE and the repression of the expression of amy TO1 gene is abolished.

Cloning, Molecular↗
PubMed1972

Polycistronic effects of catabolite repression on the lac operon.

The catabolite repression caused by glucose and glucose-6-phosphate has been studied for both beta-galactosidase and thiogalactoside transacetylase, the products of the operator proximal and distal cistrons of the lac operon, respectively. We find that both cistrons are affected coordinately by this form of repression. We also find that a single alteration at the lac promoter region is sufficient to abolish sensitivity to repression of both cistrons. From this, we conclude that there is only one target site for catabolite repression in the lac operon.

Acetyltransferases↗
PubMed1982

Nitrogen catabolite repression in a glutamate auxotroph of Saccharomyces cerevisiae.

The biosynthesis of asparaginase II in Saccharomyces cerevisiae is subject to nitrogen catabolite repression. In the present study we examined the physiological effects of glutamate auxotrophy on cellular metabolism and on the nitrogen catabolite repression of asparaginase II. Glutamate auxotrophic cells, incubated without a glutamate supplement, had a diminished internal pool of alpha-ketoglutarate and a concomitant inability to equilibrate ammonium ion with alpha-amino nitrogen. In the glutamate auxotroph, asparaginase II biosynthesis exhibited a decreased sensitivity to nitrogen catabolite repression by ammonium ion but normal sensitivity to nitrogen catabolite repression by all amino acids tested.

Amino Acids↗
PubMed1994

Effect of carbon source and extracellular pH on the acidification of the culture medium and phosphatase excretion in Neurospora crassa.

Exogenous Ca2+ at concentrations up to 3.5 mM increases the sucrose-induced acidification of the culture medium when the mold Neurospora crassa is grown on low-phosphate (Pi) medium at pH 7.8. Induction depends on the pH of the culture medium adjusted for conidial inoculation and on the absence of carbon sources generating cytoplasmic acetyl CoA. Furthermore, the excretion of Pi-repressible acid and alkaline phosphatases was not stimulated by increasing exogenous Ca2+ levels. We also provide evidence that the extracellular pH monitoring by Neurospora crassa may be a determinant in the selective excretion of Pi-repressible acid and alkaline phosphatases.

Acid Phosphatase↗
PubMed1994

Explanation for different types of regulation of arginine biosynthesis in Escherichia coli B and Escherichia coli K12 caused by a difference between their arginine repressors.

In Escherichia coli K12, formation of the enzymes of arginine biosynthesis are controlled by arginine, with complete repression during growth with added arginine, severe repression (about 95%) during growth without added arginine and complete derepression during arginine-limited growth. In E. coli B, the degree of repression is not correlated with arginine concentrations. Under all conditions of growth enzyme formation is repressed, with repression being somewhat less in a medium with arginine than in a medium without arginine. These differences in repressibility between the two strains have been shown previously to be due to the presence of different alleles of argR, the gene for the arginine repressor. Here we have compared the binding of the two repressors to the operator sites of argF (ARG boxes). In DNase I footprinting and gel retardation experiments with argF ARG boxes we have shown that the arginine repressor of E. coli K12 bound to arginine (ArgRK-arg) has a greater affinity than the arginine repressor of E. coli B bound to arginine (ArgRB-arg), whereas free ArgRB (ArgRBf) has a much stronger affinity than free ArgRK (ArgRKf). The stronger binding of ArgRBf can explain the repression seen in E. coli B during arginine-limited growth and indicates that ArgRBf, but not ArgRKf, is able to repress enzyme synthesis under physiological conditions. The weaker repression of E. coli B than of E. coli K12 seen in the presence of arginine can be explained by the lower affinity of ArgRB-arg for operator sites as compared to ArgRK-arg. Another contributing cause for the weaker repression is the reduction of ArgRBf concentration due to autoregulation of the gene for the repressor. Thus the combined effects of repression by ArgRBf, but not ArgRKf, with the weaker repression by ArgRB-arg as compared to ArgRK-arg, convert the arginine dependent regulation in E. coli K12 to arginine independent regulation in E. coli B.

Arginine↗