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Biomedical subjects

J Piette

Publications and source records attributed to J Piette.

At least 181 records · Page 10Linked to original sources
PubMed1984

DNA sequence of the carA gene and the control region of carAB: tandem promoters, respectively controlled by arginine and the pyrimidines, regulate the synthesis of carbamoyl-phosphate synthetase in Escherichia coli K-12.

The carAB operon of Escherichia coli K-12, which encodes the two subunits of carbamoyl-phosphate synthetase (glutamine hydrolyzing) [carbon-dioxide: L-glutamine amido-ligase (ADP-forming, carbamate-phosphorylating); EC 6.3.5.5], is cumulatively repressed by arginine and the pyrimidines. We describe the structure of the control region of carAB and the sequence of the carA gene. Nuclease S1 mapping experiments show that two adjacent tandem promoters within the carAB control region serve as initiation sites. The upstream promoter P1 is controlled by pyrimidines; the downstream promoter P2 is regulated by arginine. Attenuation control does not appear to be involved in the expression of carAB. A possible mechanism by which control at these promoters concurs to produce a cumulative pattern of repression is discussed. The translational start of carA is atypical; it consists of a UUG or AUU codon.

Amino Acid Sequence↗
PubMed1984

In vitro cross-linking of bovine lens proteins photosensitized by promazines.

Promazine derivatives induce cross-linking of bovine lens crystallins in vitro by irradiation with near-ultraviolet (UV) light in the presence of O2, as revealed by electrophoresis after denaturation. With the five derivatives tested (promazine [PZ], chlorpromazine [CPZ], triflupromazine [ TFPZ ], methoxypromazine [ MTPZ ], and acepromazine [ ACPZ ] ), single-hit kinetics are observed. Evidence implicating the cation radicals of the PZ derivatives as the causative agent of this in vitro effect is presented. Hydroxyl radicals do not appear to be involved in the photo-cross-linking reaction. Sodium ascorbate protects against damage induced either by PZ derivatives plus light or by PZ cation radicals in the dark. These findings are discussed with respect to development of cataracts induced by these drugs in vivo.

Acepromazine↗
PubMed1983

Molecular basis for modulated regulation of gene expression in the arginine regulon of Escherichia coli K-12.

We compare the nucleotide sequences of the regulatory regions of five genes or groups of genes of the arginine regulon of Escherichia coli K-12: argF, argI, argR, the bipolar argECBH operon and the carAB operon. All these regions harbour one or two copies of a conserved 18 bp sequence which appears to constitute the basic arginine operator sequence (ARG box). We discuss the influence of ARG box copy number, degree of dyad symmetry, base composition, and position relative to the cognate promoter site on the derepression-repression ratios of the genes of the regulon. A novel hypothesis, based on structural considerations, is also put forward to account for the absence ot attenuation control.

Arginine↗
PubMed1983

Lack of singlet oxygen formation by photoexcited promazine derivatives in aqueous and ethanolic solutions.

The EPR detection of nitroxide formation and the observation by thin layer chromatography of the specific 1O2 oxidation product of cholesterol, have been used to appreciate singlet oxygen production by promazine and four of its derivatives during irradiation with near-UV light of ethanolic and aqueous solutions. Within the range of sensitivity of the methods, no 1O2 had been detected.

Acepromazine↗
PubMed1983

Phototoxicity of phenothiazine derivatives. I. Inactivating and mutagenic effects on bacteriophage øX174.

Inactivation of øX174 bacteriophages as a function of the irradiation time in the near-UV and in the presence of triflupromazine (TFPZ), promazine (PZ), chlorpromazine (CPZ) or methoxypromazine (MTPZ) proceeds according to single hit kinetics. Acepromazine (ACPZ) has no significant activity. At low concentrations (0.1 mM) TFPZ and PZ are the most active compounds. Higher concentrations (up to 5 mM) result in a protective effect by these two compounds but cause increased inactivation rates in the case of MTPZ or CPZ. Photoinactivation mediated by TFPZ or CPZ increases the reversion frequency of a øXamber mutant. Neither MTPZ nor PZ sensitization induces mutagenesis. The effect of NaN3 on the phage inactivation rate varies depending upon both the sensitizer and the concentration of the quencher. Phage inactivation in an N2 atmosphere is measurable only in the presence of high concentrations of CPZ and MTPZ. The drugs do not show any selectivity for calf thymus DNA or bovine serum albumin, at least as measured by dialysis equilibrium experiments.

Azides↗
PubMed1983

Phototoxicity of phenothiazine derivatives. II. Photosensitized cross-linking of erythrocyte membrane proteins.

Irradiation in the presence of O2, with near-UV light of five promazine (PZ) derivatives added to erythrocyte ghost membranes, causes covalent cross-linking between proteins as revealed by a progressive decrease in the amounts of proteins separable by electrophoresis after denaturation. The induction of cross-links in the two spectrin subunits is a single-hit process as a function of the irradiation time; relatively the rate constants (in min-1) of the photoreactions were 0.060 with chlorpromazine (CPZ), 0.039 with methoxypromazine (MTPZ), 0.031 with PZ, 0.029 with triflupromazine (TFPZ) and 0.006 with acepromazine (ACPZ). A main photochemical intermediate implicated in the spectrin aggregation seems to be the cation radical of the PZ derivatives. Indeed, (i) the chemically generated cation radicals can induce the reaction in the dark; (ii) the photoaggregation is regularly reduced upon addition of increasing concentrations of NaN3; (iii) NaN3 similarly affects the amount of cross-links induced by the isolated cation radicals. Hydroxyl radicals are also involved in the photocross-linking when the reaction is initiated only by MTPZ and not by the other sensitizers. In the absence of oxygen during irradiation, PZ, MTPZ and ACPZ completely loose their cross-linking activities whereas CPZ and TFPZ remain as efficient as in the presence of oxygen.

Animals↗
PubMed1983

Activated oxygen species produced by photoexcited furocoumarin derivatives.

Furocoumarin derivatives (FCD) are investigated in order to determine their ability to photosensitize the production of activated oxygen species. Using the method based on the specific singlet oxygen (1O2) oxydation of cholesterol, all FCD except bergaten appeared to be able to produce 1O2 with various efficiencies. EPR spin trapping experiments show that photoexcited FCD produce hydroxyl radicals as detected by the formation of a DMPO-OH signal which can be abolished when the photosensitization reaction is carried out in the presence of specific OH scavengers. Moreover, the photo-ejection of hydrated electron (e-) by FCD is demonstrated by the loss of paramagnetic absorption of nitroxide free radicals as e- trap.

Cholesterol↗
PubMed1982

The regulatory region of the divergent argECBH operon in Escherichia coli K-12.

The nucleotide sequence of the control region of the divergent argECBH operon has been established in the wild type and in mutants affecting expression of these genes. The argE and argCBH promoters face each other and overlap with an operator region containing two domains which may act as distinct repressor binding sites. A long leader sequence - not involved in attenuation - precedes argCBH. Overlapping of the argCBH promoter and the region involved in ribosome mobilization for argE translation explains the dual effect of some mutations. Mutations causing semi-constitutive expression of argE improve putative promoter sequences within argC. Implications of these results regarding control mechanisms in amino acid biosynthesis and their evolution are discussed.

Base Sequence↗
PubMed1982

IS3 can function as a mobile promoter in E. coli.

We had shown previously (3) that the E. coli argE gene could be turned-on by an IS3 element inserted in orientation II near the 5' end of the gene. Here we show that this effect is due to the presence of an outward promoter located on IS3. The exact site of insertion of IS3 was determined by DNA sequencing. Using the S1 nuclease mapping technique with in vivo transcribed RNA we located the promoter responsible for argE transcription on IS3 itself outside the region involved in the inverted repeats of this element. IS3 may therefore be considered as a mobile promoter.

Base Sequence↗
PubMed1982

Homologous control sites and DNA transcription starts in the related argF and argI genes of Escherichia coli K12.

The argF and argI genes code for similar proteins able to assemble into hybrid isoenzymes and are therefore thought to share a common origin. We show here that the nucleotide sequence of the promoter and operator regions of these two genes are highly homologous. DNA regions preceding the control sites also present significant homologies. The results support the notion of divergent evolution of the two genes from a common ancestor. Like argE and argCBH , argF and argI are controlled by a repressor molecule recognizing a family of similar operator sites. Attenuation appears to play no role in this regulation.

Base Sequence↗
PubMed1982

Visible-light-induced OH radicals in DNA-proflavine complexes: an e.p.r. and spin trapping study.

Using the spin-trapping technique, irradiation with visible light of complexes between DNA and proflavine was shown to generate OH radicals. The characteristic spectra were not obtained when proflavine or DNA were irradiated alone, nor when oxygen was absent. Using DMPO as a spin trap we found that the intensity of the DMPO-OH e.p.r. signal was enhanced when the molar ratio between bound proflavine and the DNA phosphorus increased up to a value of 0.15 demonstrating the efficiency of the intercalated dye molecules. A strong decrease of the e.p.r. signal was observed in the presence of various OH. scavengers like t-butanol, isopropanol or sodium benzoate. The OH. production was also decreased when the irradiation was made in the presence of SOD, ceruloplasmin or catalase and after addition of Chelex 100 resin.

Acridines↗
PubMed1981

Mechanism for strand-break induction in DNA-proflavine complexes exposed to visible light.

Proflavine bound-superhelical phi XRFI DNA Molecules undergo single-strand scission upon irradiation with visible light at high fluence rate. As shown by agarose gel electrophoresis analyses, the nicking reaction is (i) oxygen-dependent, (ii) strongly inhibited by catalase and an electron scavenger such as cystamine, and (iii) totally suppressed by ceruloplasmin and radical scavengers such as t-butanol sodium benzoate. This indicates that H2O2, e-, O2 and OH, respectively, are involved in the cleavage process. NaN3, a singlet-oxygen quencher, has very little effect on strand-breakage but it prevents almost completely the alteration of guanine residues (a lesion already observed after irradiation at low fluence rate). Since, in the presence of NaN3, strand scission can occur and guanine (as the other bases) recovered intact, it follows that the radical intermediates produced during breakages are probably not involved in any permanent modification of the DNA bases.

Acridines↗