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C Lazdunski

Publications and source records attributed to C Lazdunski.

At least 145 records · Page 8Linked to original sources
PubMed1972

Isolation and some properties of cell envelope altered mutants of Escherichia coli.

Mutants of Escherichia coli which have a defect in their permeability barrier were selected. The technique used was to employ a strain of E. coli having a deletion in the gene for lactose permease and to select for mutants which can grow on lactose at 40 C. Twenty such mutants were isolated and six of these were found to be more sensitive to actinomycin D, sodium deoxycholate, and sodium dodecyl sulfate than was the parental strain. They were also more sensitive to the antibiotics vancomycin and bacitracin, which inhibit peptidoglycan biosynthesis. These mutants were no more sensitive to several different colicins or phages than was the wild-type strain. One of the mutants selected by this technique has an abnormal morphology when grown on certain carbon sources in minimal medium, and this mutant is more extensively studied in the accompanying paper.

Bacitracin↗
PubMed1972

Relationship between permeability, cell division, and murein metabolism in a mutant of Escherichia coli.

A mutant of Escherichia coli has been found to have an increased sensitivity to actinomycin D and to sodium deoxycholate and an unusual morphology which accompanies an abnormality in cellular division. All of these characteristics are suppressed when the strain is grown in the presence of d-alanine. This strain, called MAD-1, for murein altered division mutant, exhibits its pleiotropic phenotype only when certain carbon compounds are used as energy sources in minimal medium. Nonpermissive carbon sources, which elicit the disturbed phenotype, include glucose, mannitol, fructose, maltose, and lactose; permissive carbon sources include galactose, glycerol, lactate, and succinate. The mutant is able to transport nonpermissive carbon compounds; 3 mM 3',5'-cyclic adenosine monophosphate included in the medium does not alter the phenotype seen with growth on glucose. Deoxyribonucleic acid and protein synthesis are normal with respect to cellular mass increase. d-Alanine specifically suppresses the pleiotropic phenotype at a concentration six times lower than l-alanine, the only other compound found to be effective. There is no abnormality in the K(m) or V(max) of l-alanine racemase or d-alanine-d-alanine synthetase of MAD-1 compared to its parent, CR34. MAD-1 is more susceptible to growth inhibition by penicillin or cycloserine than its parent, and is exquisitely sensitive to lysis in the presence of sodium deoxycholate or lysozyme. When cell wall biosynthesis is inhibited, MAD-1 lyses much more rapidly than CR34, even after it has been phenotypically suppressed by growth on d-alanine. The incorporation of l-alanine and diaminopimelic acid into the peptidoglycan of the mutant and wild type is identical; d-alanine is incorporated 1.5 times more rapidly into MAD-1 cells grown under nonpermissive conditions. The peptidoglycan fragments seen after digestion with lysozyme were similar for MAD-1 and the wild type. The results are interpreted as being compatible with an increased autolytic rate in MAD-1, caused either by an increase in the quantity or activity of an autolysin, or by an abnormal cell wall which is especially susceptible to autolysis, but which was not detected by analysis of peptidoglycan fragments.

Alanine↗
PubMedDate not supplied

The maximum rate of gene expression is dependent on the downstream context of unfavourable codons.

Presented here is an experimental demonstration of our theoretical predictions on the role of the downstream context of unfavourable codons in a gene on its expression level. Six non clustered AGG codons were inserted in the chloramphenicol acetyltransferase (cat) gene of E. coli and the expression of this modified gene (cat4) was compared with that of a cat gene in which four clustered AGG codons were inserted (cat2 gene). As predicted, the rate of production of the corresponding CAT4 and CAT2 proteins is equal as long as the rate of transcription of the gene does not exceed a given limit. When this limit is exceeded, production of CAT4 continues to increase, whereas CAT2 production decreases dramatically. Various consequences and possible applications of this downstream context effect are discussed.

Base Sequence↗
PubMedDate not supplied

A genetic engineering approach to study the mode of assembly of the OmpF porin in the envelope of E coli.

Inducible hybrid genes encoding two large domains, a periplasmic domain consisting of the PhoS sequence and an outer membrane domain corresponding to various lengths of the OmpF mature sequence were constructed. The synthesized hybrid polypeptides are correctly processed during the early times of induction, their precursor forms being accumulated at later times. These hybrids restore sensitivity toward colicin A to ompF E coli B strain which suggests an outer membrane location. At least 2 of them are indeed localized in the outer membrane after immunogold labelling on ultrathin cryosections. Insertion of a hydrophobic sequence between PhoS and OmpF improves the trimerization and the assembly of the OmpF part. Only the hybrids presenting the last C-terminal 29 residues of OmpF are able to promote the colicin N killing action and to exhibit a trimeric conformation which is recognized by specific antibodies. Moreover, the deletion of the C-terminal region impairs the functional insertion of the OmpF domain; this indicates that the last membrane-spanning region of OmpF is necessary for the correct folding and orientation of the protein in the outer membrane.

Antibodies, Monoclonal↗
PubMedDate not supplied

Cytoplasmic and periplasmic expression of a synthetic gene for ferredoxin in Escherichia coli.

A synthetic gene coding for a modified ferredoxin II of Desulfovibrio desulfuricans Norway strain was assembled from 10 oligonucleotides. This gene was cloned into various expression vectors allowing either cytoplasmic expression or export to the periplasmic space. In the latter case, two different constructs were made, each of which contained the OmpA signal peptide: one of these constructs contained 3 additional N-terminal amino acids as compared to the wild-type ferredoxin (56 amino acid residues). The expression of proteins encoded by the 3 constructs was assayed in E coli and the proteins were localized by cell fractionation and immunogold labelling. A low percentage of the periplasmic ferredoxin (approximately 5%) was secreted to the medium in the absence of cell lysis. The recombinant ferredoxin was purified and found to be correctly processed by the leader peptidase. However, due to the high cysteine content intramolecular and intermolecular disulfide bonds were formed and prevented binding of [4Fe-4S] clusters. Reconstitution experiments using these recombinant proteins are in progress.

Amino Acid Sequence↗