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T Grundström

Publications and source records attributed to T Grundström.

68 records · Page 4Linked to original sources
PubMed1982

Overlap between ampC and frd operons on the Escherichia coli chromosome.

The promoter for the Escherichia coli ampC beta-lactamase gene is shown to be located within the last gene of the fumarate reductase (frd) operon. Evidence is presented that the ampC attenuator serves as the terminator for transcription of this preceding operon. The nucleotide sequence was determined for two proteins that were shown to be encoded by a DNA segment preceding the ampC gene. The two proteins consisted of 131 and 119 triplets and had molecular weights of 15,000 and 13,100, respectively. The twelve COOH-terminal amino acids of the 13,100 molecular weight protein were found to overlap the ampC promoter. Accordingly, a G.C insertion in the promoter gave both increased transcription of ampC and a frameshift in this overlapping gene, resulting in readthrough proteins. Thus, we describe a type of very compact genetic organization of operons in prokaryotes.

Base Sequence↗
PubMed1982

Location and nucleotide sequence of frdB, the gene coding for the iron-sulphur protein subunit of the fumarate reductase of Escherichia coli.

The frdB gene, encoding the iron-sulphur protein subunit of fumarate reductase, has been located and its complete nucleotide sequence determined. The identity of the gene was confirmed by protein chemical studies and determination of the NH2-terminal sequence of the FrdB protein. The frdB gene is situated distal to and partially overlapped by frdA which codes for the flavoprotein subunit of the reductase. Its reading frame contains 244 codons and predicts a protein of Mr 27092. In composition, the FrdB protein is strikingly similar to the corresponding subunit of the related flavoenzyme, succinate dehydrogenase. Analysis of the protein's primary structure revealed several features characteristic of iron-sulphur proteins.

Base Sequence↗
PubMed1981

The E. coli beta-lactamase attenuator mediates growth rate-dependent regulation.

We have identified a new control or attenuator region in the chromosomal beta-lactamase operon of Escherichia coli. A single base alteration within its attenuator led to a loss in the cell's ability to coordinate its content of beta-lactamase with growth rate. We suggest a mechanism through which this mode of regulation operates.

Base Sequence↗
PubMed1981

ampC cephalosporinase of Escherichia coli K-12 has a different evolutionary origin from that of beta-lactamases of the penicillinase type.

A 1536-nucleotide-long sequence that carries the ampC beta-lactamase gene of the Escherichia coli K-12 chromosome has been determined. This gene codes for a protein of 377 amino acids, of which the first 19 amino acids form a signal peptide. The molecular weight of the mature enzyme was determined to be 39,600. The ampC beta-lactamase with a substrate specificity for cephalosporins showed no significant sequence homologies with beta-lactamases of the penicillinase type or with D-alanine carboxypeptidases. However, because the region around serine-80 of the ampC beta-lactamase has extensive homology with an active-site fragment of the Pseudomonas aeruginosa cephalosporinase, we suggest that the ampC cephalosporinase as well as related cephalosporinases form a distinct group of serine beta-lactamases that have an evolutionary origin different from that of the serine penicillinases and thus constitute a new class of beta-lactamases.

Base Sequence↗
PubMed1980

Tandem duplication induced by an unusual ampA1-, ampC-transducing lambda phage: a probe to initiate gene amplification.

Secondary attachment site lambda-lysogens were isolated in an Escherichia coli strain carrying multiple tandem 9.8 kb repeats. The repeat carried the structural gene for chromosomal beta-lactamase, ampC. One lysogen produced lysates with amp-transducing activity. Three types of phages with different densities were obtained from this lysogen. The one with the lowest density was found to be a helper lambda cI857S7 phage. The other two phage showed identical restriction endonuclease fragmentation patterns. The difference in density was due to the presence or absence of phage tail. In lambda damp the right cohesive end segment was deleted in a random fashion with the majority ending between 81.0% and 82.4% of lambda. The chromosomal segment of lambda damp was most likely located at the lambda attachment site. The lambda damp DNA was compared to that of ColE1 hybrid carrying the chromosomal amp segment and a ColE1 hybrid carrying the same 9.8 kb amp repeat as the lysogen from which lambda damp was isolated. It was found that the chromosomal part of lambda damp constituted 9.8 kb, i.e. the size of one repeat. Moreover, the novel joint between adjacent repeats was present. In a lambda attB-deleted E. coli K-12 strain, lysogenic for lambda damp, highly ampicillin-resistant mutants occurred at an exceedingly high frequency. They were found to contain in the chromosome an amplified 9.8 kb repeat. This suggested that integration of the novel joint for lambda damp into the amp region gives rise to an amplifiable duplication. In E. coli lysogenized for lambda damp at lambda attB highly ampicillin-resistant clones were also found at a high frequency. These clones carried multiple tandem repeats of lambda damp DNA, each with an intact right end segment.

Ampicillin↗
PubMed1980

Physical mapping and expression of hybrid plasmids carrying chromosomal beta-lactamase genes of Escherichia coli K-12.

Hybrid plasmids carrying the ampC gene of Escherichia coli K-12 that codes for the chromosomal beta-lactamase were physically studied. The ampC gene was mapped to a deoxyribonucleic acid segment encompassing 1,370 base pairs. The mapping was facilitated by the isolation of a plasmid carrying an insertion of the transposable element gamma delta (gamma delta) close to ampC. The ampA1 mutation, which increases the expression of ampC by a factor of about 20, was localized to a 370-base pair segment of the 1,370-base pair deoxyribonucleic acid segment that contains the ampC gene. Using a minicell protein labeling system, it was seen that plasmids carrying either ampA+, ampC, or ampA1 and ampC coded for a 36,000-dalton protein which comigrated with purified chromosomal beta-lactamase. In cells carrying plasmids that bore the ampA1 allele, the production of this protein was greater. In addition, a protein with a slightly higher molecular weight (38,000) was expressed by both ampA+ ampC and ampA1 ampC plasmids in this protein labeling system. This protein might represent a precursor form of chromosomal beta-lactamasee. From E. coli K-12 strains carrying the ampA1 allele, second-step mutants were isolated that hyperproduced chromosomal beta-lactamase. By reciprocal recombination, plasmid derivatives were isolated that carried these mutations. Two second-step regulatory mutations mapped within the same 370-base pair region as ampA1. This piece of deoxyribonucleic acid therefore contains ampA, a control sequence region for ampC.

Cloning, Molecular↗
PubMed1980

Overproduction of outer membrane protein suppresses envA-induced hyperpermeability.

A quantitative study on outer membrane components was performed in a number of envelope mutants of Escherichia coli K-12 exhibition different permeability properties for antimicrobial agents. The envA1 allele causing an increased influx for both hydrophobic and hydrophilic drugs was found to be associated with a deficiency in the amount of lipopolysaccharides. The sefA1 envA1 double mutant was found to have a higher outer membrane buoyant density, apparently due to an increase in protein content. This double mutant was still low in lipopolysaccharide content.

Alleles↗
PubMed1980

Surface charge and hydrophobicity of Salmonella, E. coli, Gonococci in relation to their tendency to associate with animal cells.

The surface charge and hydrophobicity of Salmonella typhimurium, Escherichia coli and Neisseria gonorrhoeae bacteria have been compared with their tendency to associate in vitro with human polymorphonuclear leucocytes (PMNL) and HeLa cells in culture. It was found that lipopolysaccharide mutations in S. typhimurium or E. coli, yielding core-defective mutants, increased the surface hydrophobicity, as assessed by aqueous two-phase partitioning and hydrophobic interaction chromatography, and promoted the association with PMNL and HeLa cells. The association to HeLa cells was much smaller for the E. coli than for the S. typhimurium bacteria. All the colonial variants of N. gonorrhoeae interacted significantly with the PMNL and the HeLa cells. They were liable to hydrophobic interaction. However, the non-piliated, T3 and T4, were slightly more hydrophobic, but less negatively charged, than the piliated T1 and T2 bacteria. There was a positive correlation between possession of COA- and pili-proteins in the outer membrane and enhanced interaction with PMNL. The reverse was found with respect to association with HeLa cells. The results support the hypothesis that expression of hydrophobicity and negative charge can increase the interaction of bacteria with certain animal cells, e.g. PMNL and HeLa cells.

Escherichia coli↗
PubMed1980

Susceptibility to penicillins and cephalosporins in beta-lactamase producing strains of E. coli and relative amount of beta-lactamase produced from these strains.

The genetic and physiological mechanisms for affecting the amount of chromosomally mediated beta-lactamase of Escherichia coli K 12 was reviewed. The presence of clinical E. coli isolates with elevated beta-lactamase production was assessed. Among cephalothin resistant isolates from patients with urinary tract infections, six E. coli strains were found to produce elevated amounts of a beta-lactamase indistinguishable from that coded by the ampC gene of E. coli K 12. The resistance levels displayed by these isolates towards a number of beta-lactams was very high as compared to E. coli strains being wild type for chromosomal beta-lactamase production. Cefuroxime and to lesser extent cefamandole were stable to hydrolysis by E. coli chromosomal beta-lactamase but acted as inhibitors of the enzyme. Nevertheless increased beta-lactamase production mediated an increased resistance towards these drugs.

Cephalosporins↗
PubMed1979

Isolation and characterization of DNA repetitions carrying the chromosomal beta-lactamase gene of Escherichia coli K-12.

A ColEl hybrid plasmid, pNUl, carrying the amp operon coding for chromosomal beta-lactamase was isolated from the Clarke and Carbon collection and physically mapped. The physical location of ampC within this plasmid was further deduced by in vitro cloning. By reciprocal recombination between pNUl and chromosome of two unstable beta-lactamase hyperproducing E. coli K-12 mutants a large plasmid from each mutant was obtained. The respective plasmid was physically mapped and found to contain five and two repeated DNA segments. The repetitions within each plasmid were equal in size, 9,800 bp and 11,900 bp respectively and were organized in tandem. The end points of the repeats were different in the two plasmids but shared a DNA segment carrying the ampC gene. The chromosomal DNA of the beta-lactamase hyperproducing E. coli mutants were found to contain an amplified DNA segment equal in size to the repeated unit found in the respective plasmid. The data shows that up to 10 identical repeats organized in tandem can be generated by a normal mutation frequency in E. coli.

Cloning, Molecular↗
PubMed1977

Escherichia coli K-12 mutants hyperproducing chromosomal beta-lactamase by gene repetitions.

Escherichia coli K-12 ampicillin-resistant mutants hyperproducing chromosomal beta-lactamase arose spontaneously from strains carrying ampA1 ampC(+). Such mutants were found even in a recA background. Two Amp(r)-100 strains were analyzed genetically. The Amp(r)-100 resistance level of both strains could be transduced by direct selection for ampicillin resistance. Several classes of ampicillin-resistant transductants were found that differed from one another in the beta-lactamase activity and the ampicillin resistance mediated by an ampA1 ampC(+)-carrying strain. The data suggested that beta-lactamase hyperproduction was due to repetitions of the chromosomal amp genes. The size of the repeated region was calculated from cotransduction estimates, using the formula of Wu (Genetics 54:405-410, 1966), and was found to be about 1 min in one strain and 1.5 min in the other. Second-step Amp(r)-400 mutants were isolated from an Amp(r)-100 strain. The resistance of these mutants was apparently also due to repetitions, each mediating a resistance to about 10 mug/ml. Mutants of wild-type strains that were moderately resistant to ampicillin also gave rise to intermediate-resistance classes, suggesting repetitions of the wild-type amp alleles. F' factors hyperproducing chromosomal beta-lactamase by gene repetitions were constructed. They mediated levels of ampicillin resistance comparable to that of naturally occurring resistance plasmids. The expression of beta-lactamase hyperproduction was not affected by the presence of ampA and ampC alleles in trans and did not act in trans on the other alleles.

Alleles↗
PubMed1976

Septum formation-defective mutant of Escherichia coli.

Mutants of Escherichia coli defective in septum initiation, as well as in septum formation were obtained spontaneously, without mutagenic treatment, by selection of rifampin-tolerant mutants of an antibiotic-permeable strain carrying the envA mutation. The disturbed phenotype was in all mutants aggrevated the low incubation temperatures. One allele, sefA1, was studied in detail. Septum initiation, as well as septum formation, was promoted by high cell densities or by the addition of low concentrations of certain antibiotics, e.g., rifampin and chloramphenicol, to low-density cultures. The observed rifampicin depencence was studied in detail. These experiments indicated that a very modest shift-down situation suppressed the phenotype and enabled constrictions to proceed to cell separation. The rifampicin sensitivity of the partially purified deoxyribonucleic acid polymerase was not affected by the sefA1 allele, which is located close to proA and is thus distinct from envA. Growth parameters during the shift to 25 degrees C were followed in a transductant carrying HE SEFA1 allele. This constriction was characteristically blunt and did not lead to cell separation. At the time of formation of these frozen constrictions, clear zones representing a separation of wall from cytoplasmic membrane appeared. These polar tips did not inhibit expansion of the cell envelope. The phenotype of cells carrying the sefA1 allele suggests a disturbed relationship among protoplasm expansion, envelope growth, and septum formation. It is thought that the blunt constrictions observed are caused by an inability of the two septal peptidoglycan layers to fuse during an early stage of septation.

Cell Division↗
PubMedDate not supplied

Calcium regulation of basic helix-loop-helix transcription factors.

The basic helix-loop-helix (bHLH) family of transcription factors is essential for numerous developmental and growth control processes. The regulation of bHLH proteins occurs at many levels, including tissue specific expression, differential oligomerization and DNA binding specificities, interaction with negatively acting HLH proteins and post-translational modifications. This review focuses on what is emerging as another level of bHLH protein regulation, calcium regulation through interaction with Ca2+ loaded calmodulin and S-100 proteins. The mechanism and implications of these Ca2+ regulated interactions are discussed.

Animals↗