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Biomedical subjects

R J Warren

Publications and source records attributed to R J Warren.

At least 91 records · Page 5Linked to original sources
PubMed1969

Bacteriophage-induced inhibition of host functions. II. Evidence for multiple, sequential bacteriophage-induced deoxyribonucleases responsible for degradation of cellular deoxyribonucleic acid.

Degradation of bacterial deoxyribonucleic acid (DNA) after infection with T4 bacteriophage was studied in an endonuclease I-deficient host. The kinetics of degradation were similar to those seen in other hosts with a normal level of this enzyme. Irradiation of extracellular phage with ultraviolet (UV) destroyed the capacity of the infecting virus to induce extensive breakdown of host DNA, which was, however, converted to high-molecular-weight material. Addition of chloramphenicol to T4-infected cells provided data which can be interpreted to indicate the involvement of at least two endodeoxyribonucleases and one exodeoxyribonuclease having a high degree of specificity. A model is proposed showing the sequential action of two endodeoxyribonucleases followed by an exodeoxyribonuclease in the degradation of host DNA. The appearance of these hydrolytic enzymes requires protein synthesis. Infections leading to partial degradation only (UV-irradiated phages, gene 46 mutants) effectively inhibited the synthesis of bacterial messenger ribonucleic acid and of beta-galactosidase.

Chloramphenicol↗
PubMed1969

Properties of adenovirus messenger ribonucleic Acid synthesized in vitro.

Adenovirus deoxyribonucleic acid (DNA) was used as template for the in vitro synthesis of viral-specific ribonucleic acid (RNA). When the kinetics of the reaction were compared by using native and heat-denatured DNA templates, the latter synthesized RNA at a slower rate. The fate of the DNA after acting as template and physical characteritstics of the RNA product were studied. The DNA template, according to its sedimentation rate, was not significantly degraded by the Micrococcus lysodeicticus RNA polymerase. The products of the RNA polymerase reaction had the following properties. (i) Hybridization experiments revealed a high degree of complementarity (50 to 70%) for its homologous DNA. (ii) A very low complementarity (6 to 7%) was found for its heterologous DNA. (iii) The sedimentation rate of the synthetic RNA in a sucrose gradient was 5 to 10S when native DNA was used as the template. When heat-denatured DNA was used, the resulting RNA product, free of the template, sedimented at a rate of 3 to 16S. A rapidly sedimenting (>30S) DNA-RNA complex resulted when denatured DNA was the template. The DNA moiety of the complex was sensitive to 125 mug of deoxyribonuclease per ml. The RNA of the complex, however, was fully refractory to 50 mug of ribonuclease per ml. When the adenovirus DNA was sonically treated and then used as template, the RNA product sedimented at 3 to 9S. The heat-denatured sonically treated DNA template yielded a DNA-RNA complex that also sedimented at an unusually fast rate (>18S).

Journal Article↗
PubMed1968

Bacteriophage-induced inhibition of host functions. I. Degradation of Escherichia coli deoxyribonucleic acid after T4 infection.

The kinetics of degradation of bacterial deoxyribonucleic acid (DNA) after infection of Escherichia coli with T4D, ultraviolet-irradiated T4D, and two amber mutants, N122 and N94, was studied by zone sedimentation through linear glycerol gradients. Within 5 min after infection with any of the bacteriophages, breakdown of host genome was evident. The first product was a high-molecular-weight material (50S to 70S) and further degradation appeared to occur in discrete steps. Rapid and extensive breakdown of bacterial DNA was seen after infection with am N122 and T4D. Infection with ultraviolet-irradiated phage or with am N94 resulted in an accumulation of high-molecular-weight material. These results suggest that the observed degradation of host DNA begins early and requires sequential action of several phage-induced endo- as well as exodeoxyribonucleases.

Carbon Isotopes↗