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E Dassa

Publications and source records attributed to E Dassa.

At least 37 records · Page 2Linked to original sources
PubMed1989

Paf-acether production by Escherichia coli.

Paf is a potent mediator of inflammatory diseases and septic shock. In previous studies we showed that paf can be released by prokaryotic cells such as E. coli. In this report we define the production and release of paf by E. coli cultured under different experimental conditions. When cultures were supplemented with lyso paf, a dramatic increase in paf production was observed. Most of the paf synthesized by bacteria was released in the supernatant. Of interest C16 lyso paf was 4-fold more efficient than its C18 counterpart. Using normal and reverse phase HPLC bacterial paf exhibited physico-chemical characteristics identical to those of synthetic paf. These results may indicate that the putative E. coli acetyltransferase recognizes differently C16 and C18 lyso paf. They also could be of importance considering the pathogenetic role of enterobacteria.

Chromatography, High Pressure Liquid↗
PubMed1989

Synthesis of paf-acether from exogenous precursors by the prokaryote Escherichia coli.

Paf-acether (paf) is a potent mediator of inflammatory diseases and septic shock. Using normal-phase HPLC, a paf-like activity was found in culture supernatants from E. coli. Prokaryotic paf exhibited the same biological and physico-chemical properties as eukaryotic cells and synthetic paf. Further, reverse-phase HPLC indicates that paf generated by bacteria is predominantly of the hexadecyl and octadecyl species. When cultures were supplemented with lyso-paf, a dramatic increase in paf production was observed. The purity and molecular structure of bacterial paf were further characterized by mass spectral analysis. These results could be of importance considering the pathogenetic role of enterobacteria. Further, it appears that the competence to form and release paf is an early phylogenetic development.

Animals↗
PubMed1988

3' end of the malEFG operon in E.coli: localization of the transcription termination site.

The nucleotide sequence of a 981 bp's HincII-PvuII DNA fragment containing the 3' end of the malEFG operon in E. coli was determined. This sequence displayed a putative Rho-independent transcription termination site localized 87 bp's after the stop codon of malG. When cloned into plasmid pKG1800, the HincII-PvuII fragment containing this structure acted as a strong transcription termination signal. By S1 mapping, we demonstrated that the 3' end of the malEFG transcript coincided with the putative transcription termination site. One short open reading frames orf1 (123 bp) and and the beginning of another one orf2 were localized after malG. The transcription termination site is localized within orf1. Consequently malG is the last gene of the malEFG operon. orf2 corresponds exactly to the 5' part of the xylE gene reported independently (Davis & Henderson, 1987) as the gene coding for the XylE protein, the xylose-proton symport of Escherichia coli.

Amino Acid Sequence↗
PubMed1986

Palindromic units from E. coli as binding sites for a chromoid-associated protein.

Several hundred copies of a highly conserved extragenic palindromic sequence, 20-40 nucleotides long, exist along the chromosome of E. coli and S. typhimurium. These have been defined as palindromic units (PU) or repetitive extragenic palindromes (REP). No general function for PUs has been identified. In the present work, we provide data showing that a protein associated with a chromoid extract of E. coli protects PU DNA against exonuclease III digestion. This provides the first experimental evidence that PU constitutes binding sites for a chromoid-associated protein. This result supports the hypothesis that PUs could play a role in the structure of the bacterial chromoid.

Bacterial Proteins↗
PubMed1986

Pleiotropic mutations in appR reduce pH 2.5 acid phosphatase expression and restore succinate utilisation in CRP-deficient strains of Escherichia coli.

Several strains of Escherichia coli K12 were compared for activity of the periplasmic "pH 2.5 acid phosphatase", an enzyme whose expression is regulated negatively by cyclic AMP. Two distinct enzyme levels differing by about four-fold were observed. This strain-dependent difference does not involve modifications in the structure of the enzyme, but results from a difference in its expression. We show that strains with a high- or a low level of enzyme differ in the gene locus appR located in the 59 min region of the chromosome, a site remote from the structural gene appA; the appR+ versus appR enzyme ratio is 3-4 in wild-type strains, adenylate cyclase-deficient strains (cya) or cyclic AMP receptor protein-deficient strains (crp) grown in rich medium or in glucose minimal medium, but is close to 1 in cya strains in the presence of 0.1 mM cyclic AMP and in wild-type strains grown with succinate as carbon source; in a crp genetic background, appR strains, contrary to appR+ strains, are able to grow on minimal medium with succinate as the sole carbon source. The selection, from an appR+ crp strain, of clones growing on succinate-minimal medium, yielded mutations in the same region of the chromosome and showing the same phenotype as "naturally-occurring" appR strains. All appR strains analysed so far showed other similar deficiencies. The possibility that mutated appR gene products might function as weak substitutes for a functional cAMP-CRP complex is discussed.

Acid Phosphatase↗
PubMed1986

[Synthesis of paf-acether by E. coli K12].

Paf-acether (platelet-activating factor) is one of the most potent mediator of inflammation released from and acting on most cells that participate in inflammatory diseases. Its molecular structure is 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine. Two metabolic steps are involved in its biosynthesis: the action of a phospholipase A2 on choline-containing membrane alkyl-ether lipids results in the production of lyso paf-acether and acetylation of the lyso compound by an acetyltransferase yields the biologically active molecule. Membrane alkyl-ether lipids can therefore be considered as potential precursors of paf-acether and their composition has been studied in various cell types. In this work, we investigated the presence of paf-acether in E. coli. Our results showed that paf-acether can be obtained from E. coli K12 under a variety of bacterial growth conditions. Paf-acether from E. coli exhibited the same physicochemical and biological characteristics as synthetic paf-acether and that from eucaryotic cells. Therefore, it appears that E. coli itself has the ability of producing paf-acether, a result that could be of some importance with respect to the pathogenesis of Enterobacteria and the use of E. coli in the recombinant DNA technology.

Animals↗
PubMed1985

Sequence of gene malG in E. coli K12: homologies between integral membrane components from binding protein-dependent transport systems.

The MalG protein is needed for the transport of maltose in Escherichia coli K12. We present the sequence of gene malG. The deduced amino acid sequence corresponds to a protein of 296 amino acid residues (mol. wt. = 32 188 daltons). This protein is largely hydrophobic (hydrophobic index = 0.83) and is thus presumably an integral inner membrane protein which could span the membrane through six hydrophobic segments. We provide direct evidence from fusion proteins for the translation frame and we also identified the in vitro made MalG protein. We have found a sequence which is highly conserved between MalG and MalF, the other integral inner membrane protein of the maltose transport system. This conserved sequence is also present in all known integral membrane proteins of binding protein-dependent transport systems, always at the same distance (approximately 90 residues) from their COOH terminus. We discuss briefly this finding.

ATP-Binding Cassette Transporters↗
PubMed1985

Identification of the gene appA for the acid phosphatase (pH optimum 2.5) of Escherichia coli.

A strain of Escherichia coli exhibiting reduced activity of the periplasmic enzyme acid phosphoanhydride phosphohydrolase (pH 2.5 acid phosphatase) was isolated. The mutation designated appA1 was located at 22.5 min on the E. coli genetic map. Acid phosphatase purified from an appA- transductant showed less than ten percent of the specific activity of an isogenic appA+ strain. The mutant enzyme was highly thermolabile and its Km for paranitrophenyl phosphate was increased about 20-fold. The mutant protein cross-reacted with antibody to the wild-type enzyme and had the same molecular weight and concentration in extracts as the wild-type enzyme. These findings strongly suggest that appA is the structural gene of the acid phosphatase.

Acid Phosphatase↗
PubMed1982

The acid phosphatase with optimum pH of 2.5 of Escherichia coli. Physiological and Biochemical study.

In Escherichia coli, the physiological conditions governing the expression of an acid phosphatase with an optimum pH of 2.5 were determined. By contrast with most enzymes, the synthesis of this phosphatase was turned off in exponentially growing bacteria and started as soon as cultures entered the stationary phase. A starvation for inorganic phosphate resulted in a premature full induction, while carbon, nitrogen, and sulfur limitations were inefficient. In the presence of nonlimiting amounts of inorganic phosphate, however, the transfer of the culture to anaerobic conditions led to an immediate accumulation of the acid phosphatase. Cyclic AMP exerted a strong negative control on the biosynthesis and of this enzyme for which the integrity of both the cya and the crp gene functions was necessary. The acid phosphatase was purified to apparent homogeneity and behaved as a monomeric protein with a molecular weight of about 45,000. It had predominantly a phosphoanhydride phosphatase activity and preferentially hydrolyzed the gamma-phosphoryl residue of GTP (Km = 0.35 mM) and the 5'-beta-phosphoryl residue of ppGpp (Km = 1.8 mM). The corresponding beta-phosphoryl residue of GDP was little hydrolyzed, while CTP, ATP, and UTP were not. The enzyme did not split most phosphomonoesters with the exception of the synthetic substrate p-nitrophenyl phosphate (Km = 2.7 mM), 2,3-bisphosphoglycerate (Km = 5 mM), and fructose 1,6-bisphosphate (Km = 5 mM). It was competitively inhibited by tartaric acid and by sodium fluoride (Ki = 60 microM). In addition, it was sensitive to the inhibitor of the translation elongation factor EF-G fusidic acid, and was also strongly inhibited by the triazine dye Cibacron Blue F3GA (Ki = 0.3 microM), suggesting the existence of a site able to recognize nucleotides.

Acid Phosphatase↗
PubMed1981

ExpA: a conditional mutation affecting the expression of a group of exported proteins in Escherichia coli K-12.

A mutant of Escherichia coli K-12 was isolated as conditionally deficient in the expression of two exported proteins simultaneously (i.e. two acid phosphatases). The mutant was found to be thermosensitive on minimal medium at 37 degrees C and above, but grew normally on rich media at these temperatures. The mutation, named expA and located at 22 min on the recalibrated linkage map, depressed the levels of six periplasmic enzymatic activities in bacteria grown at 37 degrees C. At least ten proteins were greatly reduced in the periplasm under these conditions. The mutation also affected some outer membrane proteins, among which were the ompF protein and a protein which may be protein III, but had little effect on cytoplasmic membrane proteins. The gel patterns of the soluble cytoplasmic proteins were not modified except for one major protein of MW 47,000. The activities of beta-galactosidase and of aspartate transcarbamylase were unmodified. After growth at 30 degrees C no difference was observed between expA and expA+ isogenic strains. The results are discussed with respect to the mechanism of protein export.

Acid Phosphatase↗
PubMed1980

[Sulfonamide-dependent growth of a strain of Escherichia coli K12 Thy- on Mueller-Hinton medium].

The Mueller Hinton medium does not allow the growth of Escherichia coli Thy- strains. This effect is due to the presence of uridine (or a derived compound) which interferes with the function of thymidine phosphorylase. The presence of sulphonamides, in some E. coli K12 Thy- mutants, overcomes this inhibition. The same phenomenon of rescue by sulphonamides has been reproduced in a minimal medium containing thymine and uridine. The biochemical and clinical implications of this observation are discussed.

Culture Media↗
PubMed1980

The energy-dependent degradation of guanosine 5'-diphosphate 3'-diphosphate in Escherichia coli. Lack of correlation with ATP levels in vivo and role of the transmembrane proton gradient.

Different inhibitors of the energy metabolism have been assayed in Escherichia coli K12 for their ability to increase the level of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) as a consequence of a restriction of its degradation. Inhibitors of the respiration and uncouplers of oxidative phosphorylations had effects similar to carbon-source-induced downshifts while the ATPase inhibitor dicyclohexylcarbodiimide was less efficient. The effects of dicyclohexylcarbodiimide and of the uncoupler carbonylcyanide p-fluoro methoxyphenylhydrazone (FCCP) on ppGpp degradation were compared in a drug-permeable envelope mutant. At concentrations of inhibitors sufficient to deplete the pool of ATP by 50%, only FCCP was able to block ppGpp degradation. Moreover, FCCP also inhibited ppGpp degradation in a ATPase-deficient strain growing on glucose as carbon source while, as expected, it did not change the level of ATP. It is concluded, according to Mitchell's chemiosmotic hypothesis, that, in vivo, the integrity of the transmembrane proton gradient rather than the ATP pool size is a prerequisite for the normal processing of the energy-dependent degradation of ppGpp.

Adenosine Triphosphate↗