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Biomedical subjects

R C Warner

Publications and source records attributed to R C Warner.

At least 37 records · Page 2Linked to original sources
PubMed1976

Physical studies on the size and structure of the covalently closed circular chloroplast DNA from higher plants.

The size and structure of the covalently closed circular chloroplast DNAs (ctDNA) from pea, lettuce, and spinach plants, have been studied by analytical ultracentrifugation. The values of so20,w,Na+ of the native and denatured forms of the open and closed circular DNAs from these plants have been determined. The absolute molecular weight of purified closed circular pea ctDNA monomers has been determined by buoyant equilibrium sedimentation to be 89.1 (S.D. +/- 0.7)-10(6). The value of the so20,w,Na+ of open circular pea ctDNA and its molecular weight, in conjunction with corresponding values for other sizes of circular DNA, has been used to derive an empirical relationship between so20,w,Na+ and molecular weight for open circular DNAs. Using this relationship, the molecular weights of lettuce and spinach ctDNAs have been determined to be 98.2 (S.D. +/- 1.5)-10(6) and 97.2 (S.D. +/- 1.5)-10(6), respectively. At pH values 12.7 and 13, closed circular lettuce and pea ctDNAs have been found to exist as mixtures of reversibly and irreversibly denatured closed circular DNAs.

Animals↗
PubMed1976

Kinetics of branch migration in double-stranded DNA.

The rate of branch migration in double stranded DNA has been measured by the use of a unique substrate formed by the action of the EcoRI restriction endonuclease on the dimeric figure-8 configuration of the replicative form DNA of phage G4. The figure-8 and the X-form derived from it contain a junction of the kind postulated to occur in the Holliday structure and to be an essential feature of a number of models of recombination. In the X-form this junction can branch migrate to an irreversible terminal configuration consisting of two linear monomers. The disappearance of X-forms was measured by electron microscopy. A treatment of branch migration as a random walk process was developed to permit the determination of the rate of the intrinsic process, a step movement of the junction by a distance of one base pair. A value of about 6 kilobase pairs per sec at 37 degrees was obtained.

Bacteriophages↗
PubMed1975

The presence of covalently linked ribonucleotides in the closed circular deoxyribonucleic acid from higher plants.

Single-stranded scissions are induced in the covalently closed circular chloroplast (ct-) DNAs from peas, spinach, and lettuce plants by treatment with alkali or by incubation with a mixture of ribonucleases A and T1. These scissions are due to the presence of covalently linked ribonucleotides in these closed circular DNAs. By comparing the scission rates of these ctDNAs to the scission rate of RNA, it has been estimated that pea and spinach ctDNAs contain a maximum of 18 +/- 2 ribonucleotides/molecule, while lettuce ctDNA contains a maximum of 12 +/- 2 ribonucleotides/molecule. Further studies with pea ctDNA by electron microscopic methods have shown that pea ctDNA contains 19 alkali-labile sites at specific locations. A map of the relative positions of the alkali-labile sites has been constructed. These alkali-labile sites are presumably due to the insertion of individual ribonucleotides.

Alkaline Phosphatase↗
PubMed1975

Temperature and salt effects on the formation of preinitiation complexes between RNA polymerase and phage DNA.

The influence of temperature and KCl concentration on the formation of rifampicin-resistant preinitiation complexes by holo RNA polymerase has been compared for T4 DNA and Azotobacter phage A21 DNA. The sharp transition with respect to temperature between an inactive complex of polymerase and DNA and a preinitiation complex reflects an equilibrium between the two complexes, the position of which depends on the temperature and the salt concentration. The transition is shifted to higher temperatures by increasing the KCl concentration. The position of this transition is characteristically different for T4 and A21 DNA. The midpoint for A21 DNA is about 15 degrees C above that for T4 at 0.006 M KCl. At 0.15 M KCl the transition for A21 DNA cannot be observed below 37 degrees C. This difference is responsible for the apparent inhibition of a21 dna transcription by KCl and for the low template activity of A21 DNA under the conditions of the standard assay. Both holo and core RNA polymerases are able to form complexes with A21 DNA that are resistant to attack by rifampicin. The second-order rate constant for the inactivation of the complex with the core enxyme is three times greater than that for the complex with the holoenzyme.

Azotobacter↗
PubMed1975

Transcription of bacteriophage deoxyribonucleic acid. Comparison of Escherichia coli and Azotobacter vinelandii sigma subunits.

The effect of the sigma subunit of RNA polymerase on the rate and asymmetry of the in vitro transcription of Escherichia coli and Azotobacter vinelandii phage DNAs has been studied with purified E. coli and A. vinelandii RNA polymerases and hybrid enzymes containing the core subunits of one enzyme and sigma from the other. The effect of sigma on the rate of transcription is characteristic of the template and not of the enzyme and depends on ionic strength. The rate of transcription of A. vinelandii phage A21 DNA is decreased by sigma at high ionic strength, but shows the more characteristic stimulation at KCl concentrations below 0.05 M. In contrast, the stimulation by sigma of T4 DNA transcription increased with an increase in the KCl concentrations. All combinations of core and sigma subunits behaved similarly with respect to stimulation or inhibition by sigma and with respect to asymmetric transcription of S13 replicative form (RF)DNA. However, the heterologous, but not the homologous combinations of core and sigma transcribed A21 symmetrically. S13 RF DNA in the superhelical, but not in the relaxed configuration, is transcribed asymmetrically by the A. vinelandii core enzyme. A role for the core subunits in specific site recognition is indicated by this observation.

Animals↗
PubMed1975

Transcription of Azotobacter phage deoxyribonucleic acid. Salt-dependent equilibrium between steps in initiation.

The transcription of Azotobacter phage A21 DNA by Escherichia coli or Azotobacter vinelandii RNA polymerase differs from that of some other DNAs in its inhibition by moderate concentrations of KCl. This characteristic results in an apparent low template activity for this DNA as compared with T4 DNA under standard assay conditions. From an analysis of the dependence of the various steps in initiation on KCl it is concluded that the effect is exerted on an equilibrium between an inactive polymerase-DNA complex and an active preintitiation complex. This salt-sensitive equilibrium favors the inactive complex at a lower KCl concentration than with other templates. It can be approached from other low or high salt concentrations at a measurably slow rate.

Azotobacter↗
PubMed1973

Plasmids of Shigella dysenteriae Y6R: a defective Col factor.

The six plasmids of Shigella dysenteriae Y6R were separated by sucrose gradients into five fractions containing deoxyribonucleic acid (DNA), having contour lengths (expressed in units equal to the fraction of the length of the replicative form of phiX174), respectively, of 0.29, 0.35, 0.74, 1.08, and a mixture of 5.7 and 7.2. DNA-DNA hybridization on nitrocellulose filters between each of the plasmids and between plasmid-free S. dysenteriae Y6R host DNA and plasmids was investigated. There was a high degree of homology between the 0.29- and 0.35-unit plasmids. No significant homology was found between any of the other pairs of plasmids. Homologous DNA to the extent of 2.4 copies of the 1.08-unit plasmid was found in the host genome. Homology between the other plasmids and the host genome is very slight, but appears to be significant. About 0.7 of the 1.08-unit plasmid is homologous to the ColE1 façtor of Escherichia coli JC411 (ColE1). This plasmid may be defective ColE1 factor with the immunity function intact, but with a defect in the gene leading to the production of active colicin. Electron microscope examination of heteroduplexes formed between the two smallest plasmids and between the 1.08-unit plasmid and the ColE1 factor yielded independent determinations of the extent of homology in agreement with the values determined by hybridization. In the latter case, two nonhomologous regions of substitution of DNA were detected.

Centrifugation, Density Gradient↗
PubMed1969

Penicillinase plasmid DNA from Staphylococcus aureus.

A penicillinase plasmid from Staphylococcus aureus and three of its derivatives, all previously identified as extrachromosomal genetic elements, have been isolated in high yield as circular duplex DNA molecules. The wild-type plasmid was found by contour-length measurements of electron micrographs to have a molecular weight of 18.6 x 10(6) daltons. Two plasmids with deletions encompassing six and eight of the eleven known plasmid cistrons had molecular weights of 16.4 x 10(6) and 15.3 x 10(6) daltons, respectively. This information was used to establish approximate physical distances for the genetic map. A high-frequency transducing element also derived from the plasmid had a molecular weight of approximately 24 x 10(6) daltons. Although each plasmid preparation appeared homogeneous by ultracentrifugal analysis, electron micrographs always revealed the presence of a low percentage of complex oligomeric forms, particularly circular and catenated dimers.

DNA, Bacterial↗
PubMed1969

Circular deoxyribonucleic acid from Shigella dysenteriae Y6R.

Circular deoxyribonucleic acid was isolated from Shigella dysenteriae Y6R and was found to consist of six species having molecular weights of 10(6), 1.3 x 10(6), 2.6 x 10(6), 3.8 x 10(6), 20 x 10(6), and 24 x 10(6) daltons. These size classes were partially resolved by sucrose density gradient centrifugation. The minicircles (10(6) and 1.3 x 10(6)) were found to have a buoyant density in CsCl of 1.710 g/ml. The 3.8 x 10(6) dalton class had a density of 1.707 g/ml. The two largest species had a density of 1.702 g/ml. Two other strains, S. sonnei II and S. dysenteriae 60, also contained circular deoxyribonucleic acid.

Centrifugation, Density Gradient↗