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J Clow

Publications and source records attributed to J Clow.

6 recordsLinked to original sources
PubMed1991

Development and application of a multiple typing system for Clostridium difficile.

A combination of bacteriocin, bacteriophage, and plasmid typing techniques was used to differentiate strains of Clostridium difficile. A typing set of 20 bacteriocin-producing strains was established after 400 isolates of C. difficile were screened for the ability to produce bacteriocin. These strains were used to type a collection of 114 isolates of C. difficile. Forty-six (40%) of the 114 isolates were typeable, and 31 typing patterns were distinguishable. Plasmid typing of the same 114 isolates of C. difficile showed that 67 (59%) of the isolates carried up to four plasmids ranging from 7 to 60 kb in size, although most strains contained only one or two plasmids. Twenty different plasmid typing patterns were observed among the isolates. A combination of bacteriocin and plasmid typing provided 77% typeability. Fifteen (13%) of the 114 strains were typeable with five bacteriophages isolated in our laboratory, but the increase in typeability of strains over that obtainable by plasmid and bacteriocin typing was only 1.8%. Isolates that were nontypeable by bacteriocins, plasmids, or phages could be divided into two groups on the basis of positive or negative cytotoxin production. This further division of strains would increase the typeability potential by 7%; i.e., the ability to differentiate strains would rise from 77 to 84%, or perhaps 86%, if phage typing were included. We conclude that more than one of the techniques reported in this paper must be used to achieve an acceptable level of typeability of this species.

Bacterial Typing Techniques↗
PubMed1987

Effects of the Escherichia coli SSB protein on the binding of Escherichia coli RecA protein to single-stranded DNA. Demonstration of competitive binding and the lack of a specific protein-protein interaction.

The effect of the Escherichia coli single-stranded DNA binding (SSB) protein on the stability of complexes of E. coli RecA protein with single-stranded DNA has been investigated through direct DNA binding experiments. The effect of each protein on the binding of the other to single-stranded DNA, and the effect of SSB protein on the transfer rate of RecA protein from one single-stranded DNA molecule to another, were studied. The binding of SSB protein and RecA protein to single-stranded phage M13 DNA is found to be competitive and, therefore, mutually exclusive. In the absence of a nucleotide cofactor, SSB protein binds more tightly to single-stranded DNA than does RecA protein, whereas in the presence of ATP-gamma-S, RecA protein binds more tightly than SSB protein. In the presence of ATP, an intermediate result is obtained that depends on the type of DNA used, the temperature, and the magnesium ion concentration. When complexes of RecA protein, SSB protein and single-stranded M13 DNA are formed under conditions of slight molar excess of single-stranded DNA, no effect of RecA protein on the equilibrium stability of the SSB protein-single-stranded DNA complex is observed. Under similar conditions, SSB protein has no observed effect on the stability of the RecA protein-etheno M13 DNA complex. Finally, measurements of the rate of RecA protein transfer from RecA protein-single-stranded DNA complexes to competing single-stranded DNA show that there is no kinetic stabilization of the RecA protein-etheno M13 DNA complex by SSB protein, but that a tenfold stabilization is observed when single-stranded M13 DNA is used to form the complex. However, this apparent stabilizing effect of SSB protein can be mimicked by pre-incubation of the RecA protein-single-stranded M13 DNA complex in low magnesium ion concentration, suggesting that this effect of SSB protein is indirect and is mediated through changes in the secondary structure of the DNA. Since no direct effect of SSB protein is observed on either the equilibrium or dissociation properties of the RecA protein-single-stranded DNA complex, it is concluded that the likely effect of SSB protein in the strand assimilation reaction is on a slow step in the association of RecA protein with single-stranded DNA. Direct evidence for this conclusion is presented in the accompanying paper.

Adenosine Triphosphate↗
PubMed1987

Properties of the duplex DNA-dependent ATPase activity of Escherichia coli RecA protein and its role in branch migration.

We have investigated the double-stranded DNA (dsDNA)-dependent ATPase activity of recA protein. This activity is distinguished from the single-stranded DNA (ssDNA)-dependent ATPase activity by the presence of a pronounced lag time before the onset of steady-state ATP hydrolysis. During the lag phase there is little ATP hydrolysis. The duration of the lag phase, referred to as the lag time, is found to increase with the thermal stability of the dsDNA substrate. Increasing either the MgCl2 or NaCl concentration increases the lag time, whereas increasing the temperature decreases the lag time. The lag time shows little dependence on recA protein concentration but is strongly dependent on ATP concentration. After the lag phase, a steady-state ATP hydrolysis rate is achieved that approaches the rate observed with ssDNA. The steady-state phase of the reaction is proportional to the concentration of recA protein-DNA complex and shows saturation behavior at approximately equal to 5 +/- 1 base pairs per recA protein monomer. These results suggest that the lag phase represents a rate-limiting step in the dsDNA-dependent ATP hydrolysis reaction that requires a structural transition in the dsDNA and that involves a ternary complex of ATP, recA protein, and DNA. We propose that this transition involves the transient denaturation of the dsDNA to form regions of ssDNA. Elsewhere we demonstrate that the dsDNA-dependent ATPase activity is proportional to the rate of recA protein-catalyzed branch migration. We suggest that this activity is responsible for a polar polymerization that drives the branch migration reaction.

Adenosine Triphosphatases↗