Photochemical binding of anthracene and other aromatic hydrocarbons to deoxyribonucleic acid with attendant loss of tritium.
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Animals↗
Biomedical subjects
R G Fenwick
Publications and source records attributed to R G Fenwick.
Conjugal deoxyribonucleic acid replication by Escherichia coli K-12: stimulation in dnaB(ts) donors by minicells.
R64-11(+) donor cells that are thermosensitive for vegetative DNA replication will synthesize DNA at the restrictive temperature when recipient minicells are present. This is conjugal DNA replication because it is R64-11 DNA that is being synthesized and there is no DNA synthesis if minicells that cannot be recipients of R64-11 DNA are used. The plasmid DNA present in the donor cells before mating is transferred to recipient minicells within the first 20 min of mating, but additional copies of plasmid DNA synthesized during the mating continue to be transferred for at least 90 min. However, the transfer of R64-11 DNA to minicells is not continuous because the plasmid DNA in minicells is the size of one R64-11 molecule or smaller, and there are delays between the rounds of plasmid transfer. DNA is synthesized in minicells during conjugation, but this DNA has a molecular weight much smaller than that of R64-11. Thus, recipient minicells are defective and are not able to complete the synthesis of a DNA strand complementary to the single-stranded R64-11 DNA received from the donor cell.
Centrifugation, Density Gradient↗
Conjugal deoxyribonucleic acid replication by Excherichia coli K-12: effect of chloramphenicol and rifampin.
Conjugal replication of R64-11 deoxyribonucleic acid (DNA) and the concomitant transfer of R64-11 DNA to DNA-deficient minicells are dependent upon processes that are inhibited by rifampin and chloramphenicol. The rifampin-sensitive product is not present in vegetatively growing cells and is needed to initiate both conjugal DNA replication in donor cells and DNA transfer to recipient minicells. If the rifampin-sensitive product is a ribonucleic acid (RNA) molecule (rather than RNA polymerase itself), our data indicate that this RNA species required for initiation of conjugal activity does not need to be translated into a protein product. The chloramphenicol-sensitive product(s) is present in vegetatively growing cells in sufficient quantity to permit most donor cells to carry out one round of plasmid conjugal replication and transfer. The initiation of second and subsequent rounds of conjugal replication and transfer are dependent on the synthesis of both the rifampin-sensitive and chloramphenicol-sensitive products. Our results demonstrate a correspondence between the amount of conjugal DNA replication in the donor and the amount of DNA transferred to recipient minicells under all conditions, and therefore suggest but do not prove that plasmid transfer is dependent on conjugal DNA replication. The results also add additional proof that R64-11 transfer to minicells is discontinuous. All of these results are discussed in regard to further refinements of old models for the mechanism of conjugal transfer as well as a more radical departure from current dogma.
Bacterial Proteins↗
Conjugal deoxyribonucleic acid replication by Escherichia coli K-12: effect of nalidixic acid.
During the conjugal transfer of the R64-11 plasmid at 42 C from donor cells thermosensitive for vegetative deoxyribonucleic acid (DNA) synthesis to recipient minicells, the plasmids are conjugally replicated in the donor cells. This conjugal replication is inhibited by nalidixic acid, and the degree of inhibition is comparable to the reduction in the amount of plasmid DNA transferred to the recipient minicells in the presence of the drug. In addition, the size of DNA transferred to the minicells and the fraction of conjugally replicated DNA in the donor cells that can be isolated as closed-circular plasmid DNA under alkaline conditions are both reduced by nalidixic acid. When the drug is added to a mating that is underway, the rate of conjugal replication is immediately reduced. This change is accompanied by a reduction in the amount of conjugally replicated DNA in the donor cells that can be isolated as closed-circular plasmid DNA. Furthermore, conjugally replicated plasmid DNA that is not associated with the donor cell membrane becomes membrane bound after the addition of nalidixic acid.
Centrifugation, Density Gradient↗
Synthesis of ribonucleic acid and protein in plasmid-containing minicells of Escherichia coli K-12.
Unlike the deoxyribonucleic acid (DNA)-deficient minicells produced by F(-) parents, minicells produced by plasmid-containing strains contain significant amounts of plasmid DNA. We examined the ability of plasmid-containing minicells to synthesize ribonucleic acid (RNA) and protein. In vivo, minicells produced by F(-) parents are unable to incorporate radioactive precursors into acid-insoluble RNA or protein, whereas minicells produced by F', R(+), or Col(+) parents are capable of such synthesis. Using a variety of approaches, including polyacrylamide gel analysis of the RNA species produced and electron microscope autoradiography, we demonstrated that the synthesis observed in minicell preparations is a property of the plasmid-containing minicells and not a result of the few cells (approximately 1 per 10(6) minicells) contaminating the preparations. That the observed synthesis is of biological importance is suggested by the ability of plasmid-containing minicells to yield viable phage upon infection with T4.
Ampicillin↗
Temperature-sensitive hypoxanthine-guanine phosphoribosyltransferase in mutant Chinese hamster cells.
By selecting variants of Chinese hamster cells that were resistant to 6TG at 39 degrees C, but which would continue to grow in HAT medium at 33 degrees C, we have isolated cell lines with thermosensitive phenotypes for HGPRT controlled properties. THE HGPRT produced by those clones is temperature sensitive. These results indicate that the selected clones carry missense mutations in the structural gene for the enzyme.
Aminopterin↗