PubMed Health⌕ Search

Biomedical subjects

T Edlund

Publications and source records attributed to T Edlund.

At least 55 records · Page 3Linked to original sources
PubMed1987

A mutational analysis of the insulin gene transcription control region: expression in beta cells is dependent on two related sequences within the enhancer.

Cell-specific expression of the insulin gene is controlled by cis-acting DNA sequences located within approximately equal to 350 base pairs of the 5' flanking DNA immediately upstream from the transcription start site. Using synthetic oligonucleotides, we have constructed a systematic series of block replacement mutants spanning this region. No single sequence appears to be absolutely required for expression. However, three of the mutants exhibit 5-10 times less activity and several others show 2-3 times less. Simultaneous mutation of two of the most mutationally sensitive regions leads to virtual abolition of activity. These two elements are structurally related and presumably represent key components of the machinery determining the cell-specific expression of the insulin gene.

Animals↗
PubMed1986

Sequence-specific interactions of nuclear factors with the insulin gene enhancer.

Insulin 5'-flanking DNA contains two elements controlling cell-specific expression, one a cell-specific enhancer. We show that factors in nuclear extracts derived from an insulin-secreting cell line interact with three distinct regions within the insulin enhancer. The 5' border of the farthest upstream protected region coincides with the 5' border of the enhancer element, indicating a functional role for this interaction in insulin gene transcription. This protected region covers 46 bp, including an enhancer core sequence. This region was not protected in nuclear extracts prepared identically from two heterologous cell lines, indicating at least a 3-fold lower level of interacting factors in these cells. The size of this protected region suggests that more than one factor is binding, possibly facilitating cell-specific interaction of a binding protein with the core enhancer nucleotides. The other two protected regions were observed in extracts prepared from one or both of the heterologous cells.

Animals↗
PubMed1985

Cell-specific expression of the rat insulin gene: evidence for role of two distinct 5' flanking elements.

The 5' flanking DNA of the rat insulin I gene contains sequences controlling cell-specific expression. Analysis of this region by replacement of specific portions with nondiscriminatory control elements from viral systems shows that a transcriptional enhancer is located in the distal portion of the 5' flanking DNA; its position has been mapped by deletion analysis. Additional experiments suggest that another distinct regulatory element is located more proximal to the transcription start site. The activity of both elements is restricted to pancreatic B cells. The combinatorial effect of multiple control elements could explain the cell-specific expression of insulin genes.

Acetyltransferases↗
PubMed1985

Differential expression of interferon genes in a substrain of Namalwa cells.

A substrain of Namalwa cells producing a high ratio of beta-interferon (IFN-beta) versus alpha-interferon (IFN-alpha) was investigated by constructing a cDNA library after induction with Sendai virus. The library was screened by two synthetic oligonucleotides, one specific for IFN-alpha and one complementary to both IFN-alpha and IFN-beta. Rescreening the library with two full-length cDNAs encoding IFN-alpha and IFN-beta, respectively, revealed that the frequency of the IFN-alpha and IFN-beta clones reflected the activities of IFN-alpha and IFN-beta obtained by functional assays. On the cDNA level, the dominating species was identical with the type of IFN-alpha A or IFN-alpha 2; however, one new type of cDNA also was found that was similar to the previously described IFN-alpha C. Only one type of cDNA was found encoding IFN-beta, although several IFN-beta proteins have been detected in the analyzed cell line.

Base Sequence↗
PubMed1984

Novel cluster of alpha-interferon gene sequences in a placental cosmid DNA library.

A human cosmid library was constructed and probed with a human alpha interferon (IFN-alpha) cDNA clone. One clone giving a strong hybridizing signal was isolated and characterized. The cosmid DNA insert represents a section of the human genome containing three regions of IFN-alpha-like sequences. The DNA was characterized with restriction endonuclease mapping, thereby allowing comparison to similar linkage groups reported recently and determination of homologous regions on the known physical map. The three IFN-alpha-like sequences were analyzed by a partial sequence analysis. Mapping and sequence data establish this section as a not-yet-described cluster of IFN-alpha sequences in the human genome; however, a part of the section matches to some degree to a previously described genomic region. The region described here could represent genetic polymorphism or a duplicated segment.

Base Sequence↗
PubMed1983

Insect immunity. Isolation of cDNA clones corresponding to attacins and immune protein P4 from Hyalophora cecropia.

Diapausing pupae of the Cecropia moth (Hyalophora cecropia) respond to an injection of live bacteria by the selective synthesis of certain types of RNA and immune proteins (designated P1-P9). The in vitro translation products of RNA from both injured and infected pupae showed specific patterns with a defined number of extra bands. Some proteins characteristic of the normal RNA were reduced in the immune RNA translation products. Antibody reaction was used to show the selective synthesis of immune proteins P4 and P5 with mRNA from pupae subjected to injury or infection. The protein synthesized in vitro, which cross-reacted with P5 antibodies, is most likely a precursor of the attacins described in the preceding paper. A cDNA clone bank was prepared and two clones were isolated and shown to contain 750 bp corresponding to P4 and 250 bp of attacin information. These clones were used to estimate the sizes of the mRNAs by Northern blotting and to estimate, by RNA/DNA hybridization, the levels of P4 and P5 mRNA. In vivo incorporation of [35S]methionine into attacins and P4 during different conditions was compared with the levels of the corresponding mRNA.

Animals↗
PubMed1983

Isolation of cDNA sequences coding for a part of human tissue plasminogen activator.

We have isolated a cDNA sequence coding for a part of human tissue plasminogen activator. mRNA coding for tissue plasminogen activator was partially purified, copied into double-stranded cDNA, and cloned into Escherichia coli. Two sets of partially overlapping oligodeoxynucleotide mixtures corresponding to all possible coding sequences for a known portion of the tissue plasminogen activator gene were prepared. One set was used as a probe to screen cDNA containing bacterial clones and both were used as probes in hybridization against purified plasmid DNA. Of 4,200 bacterial clones examined, 1 carried a plasmid that hybridized to both sets of oligonucleotides. This plasmid contained a 370-base-pair cDNA insert, which was shown by nucleotide sequence analysis to code for the cleavage site region in the one-chain form of the human tissue plasminogen activator.

Amino Acid Sequence↗
PubMed1983

Overlapping genes.

Explore the source record for details and available documents.

Base Sequence↗
PubMed1981

Recombination between short DNA homologies causes tandem duplication.

The ampC gene of Escherichia coli K-12 codes for a beta-lactamase which can hydrolyse the beta-lactam ring of ampicillin. Ampicillin resistance is strictly related to ampC gene copy number thus we have been able to isolate ampicillin-resistant mutants carrying multiple ampC repeats. We have isolated on a plasmid a segment of chromosomal DNA carrying multiple ampC repeats, and compared the nucleotide sequence of the region joining repeat units to the sequence of the DNA segments that fused to create the joint. The fusion had occurred within a 12-base pair (bp) sequence of perfect homology. We suggest that recombination between randomly occurring short homologies (12-13-bp long), could be a general mechanism to generate tandem duplications in the size range of 10 kilobases (kb).

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↗
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↗
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

Evidence for two immune inhibitors from Bacillus thuringiensis interfering with the humoral defense system of saturniid pupae.

Mutants of Bacillus thuringiensis lacking either beta-exotoxin or gamma-endotoxin were compared for their virulence using pupae of a giant silk moth. Known doses of viable log-phase bacteria were injected, and the response was followed as the number of viable bacteria in the hemolymph. The results obtained imply that, in the system used, neither the beta-exotoxin nor the gamma-endotoxin and the sporeforming ability are of importance for virulence. Results with sterile culture filtrate from B. thuringiensis have given evidence for the production of two inhibitors, A and B, which interfere with the humoral defense system in pupae of Hyalophora cecropia. Inhibitor A, which blocked the lysis of Escherichia coli,was precipitated by trichloroacetic acid and sensitive to heating. Inhibitor B, which blocked the killing of Bacillus cereus, was soluble in trichloroacetic acid and resistant to 90 degrees C for 5 min. Both inhibitors are believed to contribute to the insecticidal nature of B. thuringiensis.

Animals↗