Expression of thymidine kinase variants is a function of the replicative state of cells

The expression of different variants of thymidine kinase (TdR kinase), characterized by electrophoretic mobilities, is related to the replicative state of normal or transformed cultured cells rather than the developmental state of the tissue of origin. The form of thymidine kinase found in actively growing cultured cells, corresponding to the “fetal kinase” of embryonic tissue, migrates as a slow moving species with an Rf of 0.20 on acrylamide gels. The “adult kinase” found in adult tissue or other nongrowing cells migrates as a faster species with an Rf of 0.50 on acrylamide gels.     

Polyuridylic Acid-directed Phenylalanine Incorporation in Minicell Extracts

Cell-free extracts of miniature Escherichia coli cells deficient in deoxyribonucleic acid (DNA) and DNA-dependent ribonucleic acid polymerase have been shown to be capable of polyuridylic acid-directed [(14)C]phenylalanine incorporation.     

Purification and Chemistry of Bacteriophage ?

From a stock of varkappa phage grown on Salmonella, a host-range mutant which attacks Escherichia coli was isolated. As in the case of Salmonella, only motile strains of E. coli are sensitive to varkappa. The phage shows an eclipse period of 35 min and a minimal latent period of 52 min. The adsorption rate constant is 3 x 10(-9) ml/min. Adsorption shows a marked dependence on temperature. Bacteriophage varkappa was purified by differential centrifugation and CsCl density gradient centrifugation. It contains deoxyribonucleic acid (DNA) which is double-stranded. The DNA has a molecular weight of 42 million and a guanine plus cytosine content of 57%. Of 68 molecules of DNA inspected, 7 were circular. The phage particle weight is about 90 million.     

Growth and Division of Filamentous Forms of Escherichia coli.

Adler, Howard I. (Oak Ridge National Laboratory, Oak Ridge, Tenn.), and Alice A. Hardigree. Growth and division of filamentous forms of Escherichia coli. J. Bacteriol. 90:223-226. 1965.-Cells of certain mutant strains of Escherichia coli grow into long multinucleate filaments after exposure to radiation. Deoxyribonucleic acid, ribonucleic acid, and protein synthesis proceed, but cytokinesis does not occur. Cytokinesis (cross-septation) can be initiated by exposure of the filaments to pantoyl lactone or a temperature of 42 C. If growing filaments are treated with mitomycin C, nuclear division does not occur, and nuclear material is confined to the central region of the filament. Cytokinesis cannot be induced in mitomycin C-treated filaments by pantoyl lactone or treatment at 42 C.     

Characterization of Clostridium perfringens (welchii) Isolated from Market Poultry

Strains of Clostridium perfringens capable of producing heat-resistant spores, characteristic of the food-poisoning types, were not recovered in a random survey of feces and livers of market poultry. Favorable growth response with a known food-poisoning strain indicated that the media and methods employed were adequate. Spores produced in vitro from this strain survived at 100 C for several hours. Animal feeding experiments with this strain showed that heat-resistant spores (surviving for 1 hr at 100 C) could be readily demonstrated 24 hr after oral instillation of vegetative cells in mouse feces, but not in chicken feces. One experiment suggests that this strain might adapt to the environment of the intestinal tract of chickens, but not all of the spores recovered were as heat resistant as those of the parent culture.     

Comparison of single and multiple treatment regimens in the mouse bone marrow micronucleus assay for hydroquinone (HQ) and cyclophosphamide (CP)

Three experiments are reported as a contribution to the validation of the multiple treatment protocol presently under discussion. (1) In the single treatment experiment with hydroquinone (HQ) the time of maximum micronucleus response was determined to be 24 h with a dose of 75 mg/kg given intraperitoneally. In the subsequent dose-response study at the 24-h interval the lowest positive dose was 50 mg/kg of HQ (P less than 0.01). The increase in micronucleus frequencies was non-linear. (2) Daily treatments with 15 or 75 mg/kg of HQ and bone marrow sampling on days 2-4 after the start of treatment resulted in an increased micronucleus yield for the lower dose (P less than 0.05) and a decrease in micronucleus frequencies at the higher dose (P less than 0.01) with increasing numbers of treatments. At the same time no change in the composition of the erythrocyte population was observed. (3) With 25 mg/kg of cyclophosphamide (CP) the micronucleus yields increased from 1 to 3 daily doses but dropped significantly from 3 to 4 daily doses (P less than 0.01). The polychromatic to normochromatic erythrocyte ratio was significantly decreased after single (P less than 0.01) and marginally lower than the control value after 4 daily treatments with CP. The present data suggest that the response of the bone marrow micronucleus assay to multiple treatments may depend on the dose employed and may differ from chemical to chemical. The specific clastogenic action or other cellular effects of a chemical may influence the micronucleus yields of an individual chemical and it may be difficult to generate a strict protocol recommendation.