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M So

Publications and source records attributed to M So.

At least 91 records · Page 5Linked to original sources
PubMed1983

Characterization of the gene encoding heat-stable toxin II and preliminary molecular epidemiological studies of enterotoxigenic Escherichia coli heat-stable toxin II producers.

The gene encoding heat-stable toxin II (STII) was cloned into an Escherichia coli K-12 strain, and its nucleotide sequence was determined. The deduced amino acid sequence indicates that STII is synthesized within the cell as a 71-amino-acid protein and that neither the DNA nor amino acid sequence bears any similarity to that of heat-stable toxin I. A DNA fragment containing the STII gene was used to probe enterotoxigenic E. coli clinical isolates with various toxin phenotypes and was shown to be useful in detecting all STII and only STII producers.

Amino Acid Sequence↗
PubMed1983

Electrophoretic study on the DNA-breaking actions of ascorbic acid and triose reductone in the presence of Cu2+.

The mode of DNA-breaking actions of ascorbic acid (AsA) and triose reductone (TR) in the presence of Cu2+ was studied by use of 0.8% agarose slab gel electrophoretic analysis. The DNA-breaking actions of the mixture of AsA or TR and Cu2+ were inhibited by N2 gas, hydroxyl radical scavengers and catalase, indicating that the oxidation of AsA or TR by Cu2+ and the hydrogen peroxide and hydroxyl radicals resulting from the oxidation are essential for the fragmentation of DNA by the mixture of AsA or TR and Cu2+. However, the DNA-breaking activity of these reductones varied with pH, while their oxidation rates were proportional to the increase in pH. The marked fragmentation of DNA occurred at pH 4, 7 or 8. The breakages of DNA by AsA or TR in the presence of Cu2+ were concluded not to be associated with the oxidation rates of reductones.

Animals↗
PubMed1983

Function of Cu2+ on the DNA-breaking actions of ascorbic acid and triose reductone.

The role of Cu2+ on the DNA-breaking action of ascorbic acid (AsA) and triose reductone (TR) was studied with an agarose slab gel electrophoretic analysis. AsA and TR decomposed calf thymus DNA which had been pretreated with Cu2+, and their decomposing activity was proportional to the concentration of Cu2+ bound to the DNA. The DNA-Cu2+ complex had the ability to oxidize reductones. AsA and TR also decomposed the pretreated DNA with Cu2+ more markedly than that pretreated with Cu2+ and successively with EDTA. The DNA-breaking activity of AsA and TR showed no Cu2+-concentration dependency. The maximal fragmentation of DNA occurred at the concentration ratio of DNA and Cu2+ of 4:1. Excess concentration of Cu2+ decreased the activity of reductones. The present results indicate that the binding of Cu2+ to DNA molecules is also essential for the DNA-breaking action of AsA and TR in the presence of Cu2+ and that Cu2+ bound to DNA molecules has more effective promoting activity than free Cu2+.

Animals↗
PubMed1983

lambda DNA-fragmenting actions of ascorbic acid and triose reductone in the presence of Cu2+.

Lambda DNA-fragmenting actions of ascorbic acid (AsA) and triose reductone (TR) in the presence of Cu2+ were studied. The mixture of AsA or TR and Cu2+ caused a marked fragmentation of lambda DNA (3.2 X 10(7) daltons) within the first 1 min of reaction. Further incubation resulted in accumulation of the most abundant species of fragmented lambda DNA having a molecular weight of 1.3 X 10(5) daltons. The mixture of AsA or TR and Cu2+ fragmented calf thymus DNA to produce the fragmented DNA of which 5'-OH terminal groups have a mixture of free OH groups and phosphodiester linkage. The mixture of AsA or TR and Cu2+ was also found to fragment lambda DNA to produce dCMP predominantly as 5'-OH terminal nucleotides.

Adenosine Triphosphate↗
PubMed1982

Pilus expression in Neisseria gonorrhoeae involves chromosomal rearrangement.

The Neisseria gonorrhoeae pilus protein is one of the major antigenic determinants on the cell's surface. It is comprised of identical subunits of approximately 18 kd and plays a role in the infectivity and virulence of the organism. We have cloned the gene encoding a gonococcal pilus protein into Escherichia coli, and, using one of these clones as a probe in hybridization studies, we have shown that conversion of the pilus positive to pilus negative state in N. gonorrhoeae involves chromosomal rearrangement. Although the pilus protein is produced by E. coli, it does not appear to be assembled on the surface of the cell in native form.

Bacterial Proteins↗
PubMed1980

Nucleotide sequence of the bacterial transposon Tn1681 encoding a heat-stable (ST) toxin and its identification in enterotoxigenic Escherichia coli strains.

the Escherichia coli heat-stable toxin (ST I) is encoded within a transposon (Tn1681) flanked by inverted repeats of insertion sequence 1 (IS1) [So, M., Heffron, F. & McCarthy, B. J. (1979) Nature (London) 277, 453-456]. By subcloning restriction fragments and by insertion mutagenesis, we located precisely the gene for ST I within the transposon. We determined the complete nucleotide sequence of the central portion of Tn1681 (i.e., that part flanked by IS1) and identified the coding sequence of the toxin. From the nucleotide sequence, we deduced a probable amino acid sequence for ST I. The NH2-terminal portion of the amino acid sequence is extremely hydrophobic and bears a striking resemblance to the signal sequence of the fd phage minor coat protein. By using a subcloned restriction fragment containing the gene for ST I but no IS1 sequences, we determined (i) that the ST toxin with activity assayable in suckling mice (ST I) is genetically distinct from the St toxin assayable in ligated ileal loops (ST II) and (ii) that ST I can be responsible for diarrheal disease in different animals.

Amino Acid Sequence↗
PubMed1980

Detection of enterotoxigenic Escherichia coli by DNA colony hybridization.

A method fo detecting large numbers of isolates of enterotoxigenic Escherichia coli is described in which the genes encoding th enterotoxins are detected, rather than the toxins themselves. Radiolabeled fragments of DNA encoding the heat-labile (LT) or heat-stable (ST) toxins were used as hybridization probes for homologous DNA sequences in E. coli colonies grown and lysed in situ on nitrocellulose filters. The LT probe detected all of 31 E. coli strains producing ST and LT or only LT, while the ST probe detected 12 of 17 strains producing only ST and three of 26 strains producing ST and LT. These results suggest that the LTs produced by different isolates of E. coli are homologous and that human isolates of E. coli produce at least two heterologous STs detectable in the infant mouse assay. The hybridization method also detected the presence of enterotoxigenic E. coli in bacterial growth in directly spotted stools from patients with acute diarrhea.

Acute Disease↗
PubMed1979

The E. coli gene encoding heat stable toxin is a bacterial transposon flanked by inverted repeats of IS1.

Restriction endonuclease subclones of the Escherichia coli gene encoding the heat stable (ST) toxin exhibit a stem and loop structure similar to those seen in many procaryotic transposons. An EcoRI DNA fragment encoding tetracycline (Tc) resistance but no transposition functions was spliced into the ST gene in one of these subclones. By monitoring Tcr, we were able to show that the ST gene transposes. Restriction and DNA sequence data strongly suggest that the ST transposon, Tn 1681, is flanked by inverted repeats of IS1.

Bacterial Toxins↗
PubMed1978

In vitro mutagenesis of a circular DNA molecule by using synthetic restriction sites.

A method for mutagenizing circular DNA molecules has been developed that uses synthetic oligodeoxynucleotide restriction sites as mutagens. A single synthetic restriction site is introduced at random by cleaving circular DNA with a nonspecific double-strand endonuclease. The restriction site is then ligated to the ends and the molecule is subsequently recircularized. These small additions to the genome are mapped by digestion with the appropriate restriction enzyme. Rearrangements such as duplications and deletions can be engineered at will by using the added restriction sites. This technique has been used to produce a fine-structure map of RSF1050, a ColE1 derivative, 60% of which is a transposable DNA sequence encoding the TEM beta-lactamase (Tn3). A subset of the mutations, mapping within a narrow region of Tn3, result in an increased frequency of Tn3 transposition; mutations in other regions abolish transposition entirely.

Bacteriocin Plasmids↗
PubMed1978

Characterization of an Escherichia coli plasmid encoding for synthesis of heat-labile toxin: molecular cloning of the toxin determinant.

P307 is a plasmid isolated from a strain of Escherichia coli that was responsible for an outbreak of diarrheal disease in piglets. This 60 X 10(6)-dalton plasmid was subsequently shown to encode for the synthesis of a heat-labile toxin (LT). Using recombinant DNA technology, we isolated a 7.8 X 10(6)-dalton DNA fragment that contains the LT gene(s). This fragment was generated using an EcoRI partial digestion of P307 DNA, and the fragment was joined to a small multicopy plasmid, RSF2124. E. coli strains harboring the chimeric plasmid produced greater amounts of LT than did the same strains containing P307. The LT genes were also isolated on a 5.8 X 10(6)-dalton DNA fragment made by BamHI digestion, and we identified an EcoRI recognition sequence that is located in a position essential for LT synthesis.

Animals↗
PubMed1978

Method for the genetic labeling of cryptic plasmids.

A recently developed method for detecting transposition was employed to genetically "label" conjugative plasmids such as F and Ent P307, which do not normally exhibit a readily identifiable phenotype.

Conjugation, Genetic↗
PubMed1976

Molecular cloning of an Escherichia coli plasmid determinant than encodes for the production of heat-stable enterotoxin.

A conjugative plasmid, ESF0041 was isolated from an enterotoxigenic strain of Escherichia coli from calves. ESF0041 was found to be 65 x 10(6) daltons in mass of a member of the F incompatibility complex. Acquisition of ESF0041 by E. coli K-12 was invariably associated with the capacity to produce heat-stable (ST) enterotoxin. ESF0041 and pSC101 deoxyribonucleic acids were cleaved with EcoRI, and the fragments were ligated with polynucleotide ligase. Transformation of E. coli K-12 with the ligation mixture led to the isolation of an ST+ clone. Further analysis of the plasmid deoxyribonucleic acid from this clone showed that a structural gene(s) associated with ST biosynthesis had been isolated as a 5.7 x 10(6)-dalton ESF0041 fragment in pSC101. In turn, 5.7 x 10(6)-dalton fragment was ligated to a multicopy COLE1 derivative, RSF2124, so that toxin synthesis was amplified about threefold.

DNA Replication↗
PubMed1975

The generation of a ColE1-Apr cloning vehicle which allows detection of inserted DNA.

A 3.2 Mdal sequence of DNA, TnA, which contains the ampicillin (Ap) resistance determinant has been translocated from an R plasmid to the plasmid ColE1. A total of 12 isolates were studied. There are at least 8 sites in ColE1 at which TnA has inserted. Insertion at five of these has resulted in a Col-phenotype. One ColE1-Apr plasmid, RSF2124, was examined further and its replication properties are found to be similar to that of the parent plasmid. RSF2124 appears to be a useful plasmid vehicle for the molecular cloning of DNA from diverse prokaryotic sources: it codes for readily detectable Ap resistance and contains a single EcoRI site in a gene affecting colicin biosynthesis so that it is unable to produce colicin upon ligation to other DNA.

Ampicillin↗
PubMed1975

Polynucleotide sequence relationships among Ent plasmids and the relationship between Ent and other plasmids.

Deoxyribonucleic acid-deoxyribonucleic acid hybridization studies reveal that the plasmids coding for the production of heat stable and heat labile enteroxtoxins of Escherichia coli, regardless of their origin, have a majority of their polynucleotide sequences in common, but are not related in any significant way to those plasmids coding for the synthesis of only ST toxin. The heat stable and heat labile plasmids also share a significant degree of their polynucleotide sequences with plasmids of the FI and FII incompatibility groups, but not with R factors belonging to the I, N, W, P, or X incompatibility groups.

Animals↗