DNA Of Chinese Hamster Cells Research Articles

Temporal organization of DNA in chinese hamster cells: Cell-cycle dependent association of DNA with membrane

DNA-lipoprotein (membrane) complexes were isolated from line CHO cells by sarkosyl crystal formation or by discontinuous gradient sedimentation analysis of sonicated cells. Less than 10 % of the DNA in the complexes was due to nonspecific interaction. Ribonuclease was without effect upon the complexes, while heating at temperatures in excess of 37 °C or treatment with deoxyribonuclease, Pronase, or sodium dodecylsulfate removed the DNA, and the latter two agents solubilized the choline-labeled membrane as well. Nearly 70 % of the newly replicated DNA (short pulse-label with [ 3H]thymidine) was associated with the complexes, and much of the new DNA could be removed from complexes by chasing in unlabeled thymidine. Although DNA was associated with membrane throughout the entire cell cycle, there was an increased amount of DNA complexed to membrane specifically during S phase. These results suggest that DNA-membrane complexes may play a role in both spatial and temporal organization of DNA during the cell cycle.

Replicon origins in Chinese hamster cell DNA: I. Labeling procedure and preliminary observations

Fluorodeoxyuridine and aminopterin, commonly used to synchronize animal cells at the beginning of S phase, are shown to be unsuitable for studying the origins of replicons because of their unsatisfactory action as DNA synthesis inhibitors, whereas hydroxyurea is suitable for this purpose. Moreover, the results presented support the bidirectional model for DNA replication in animal cells and suggest that the timing of initiation of various origins is independent of the rate of synthesis at each replication fork.

Loss of simian virus 40 DNA-RNA hybrids from nitrocellulose membranes; implications for the study of virus--host DNA interactions.

Complete hybrids of simian virus 40 (SV40)DNA and its complementary RNA (cRNA) are not retained on nitrocellulose membranes. At saturating cRNA concentrations, retention of the hybrids indicates incomplete homology between DNA and RNA, probably due to incorporation of host DNA in the viral DNA; this effect is most pronounced when DNA is produced in cells infected at high multiplicity. Hybrids between DNA of Chinese hamster cells transformed by SV40 and cRNA are retained if the DNA fragments are long, but they are lost if the DNA is sheared to less than the length of an SV40 DNA molecule. Hence, in cells examined with about six SV40 genomes per cell, each genome is individually integrated. The results may explain previous discrepancies in the estimation of the number of viral genomes in transformed cells.

Radiation-induced strand breakage in mammalian cell DNA. I. Enhancement of single-strand breaks by chemical radiosensitizers.

SummaryChinese hamster cells irradiated with x-rays in complete medium while attached to glass surfaces and equilibrated with either air or nitrogen have been subsequently assayed for both colony-forming ability and size distribution of single-strand DNA fragments. Compounds evaluated for their ability to radiosensitize hypoxic cells and the concentrations used were: 1 mM para-nitroacetophenone (PNAP), 500µM N-(5-nitro-2-furfurylidine)-1-aminohydantoin (nitrofurantoin or NF2), 500µM 5-nitrofuraldehyde-2-semicarbazone (nitrofurazone or NF1), and 500µM 5-nitrofuraldehyde-2-oxime (nifuroxime or NF3). D0 values of 323, 227, 179, 155, 160, and 105 rads were obtained for N2, N2 + 1 mM PNAP, N2 + 500µM NF2, N2 + 500µM NF1, N2 + 500µM NF3, and air, respectively, which give enhancement ratios [ER(Survival)] of 1·00, 1·45, 1·80, 2·09, 2·01 and 3·08, respectively, for these conditions. The values of electron volt / single-strand break determined from alkaline sucrose sedimentation analyses for N2, N2 + 1 mM PNAP, N2 + 500µM NF2, N2 + 500µM NF1, N2 + 500μM NF3 and air were 284, 155, 109, 92, 82 and 83 which give enhancement ratios [ER(eV/SSB)] of 1·00, 1·83, 2·61, 3·08, 3·47 and 3·44, respectively. These data show that, within experimental error, the relative effectiveness of these compounds and molecular O2 as radiosensitizers of strand breakage in DNA of Chinese hamster cells is reflected at the level of cell survival.

Distribution of DNA in Chinese hamster cells

The distribution of DNA in the nucleus of Chinese hamster cells growing in vitro was studied by labeling DNA with tritiated thymidine before cutting 20–25 serial sections through the nucleus. Autoradiography and light microscopy were used to locate the distribution of label in each section. When all of the DNA in the cell was labeled by allowing the cells to incorporate tritiated thymidine for 3–4 replication cycles, the distribution of DNA in the nucleus was characteristically peripheral. However, in about 16 per cent of the cells, the DNA was widely dispersed with a considerable amount of DNA centrally distributed within the nucleus. Following a 10-min labeling, the DNA was widely dispersed in about 30 per cent of the cells; after 4 hr of incubation, the percentage decreased rapidly to less than 5 and by 6–7 hr increased again to 20.

STUDY OF PYRIMIDINE DIMERS IN MAMMALIAN CELLS SURVIVING LOW DOSES OF ULTRAVIOLET RADIATION*

Abstract— Ultraviolet‐induced pyrimidine dimers were not found to be excided from the DNA of Chinese hamster cells in small oligounucleotides. At doses whereby many cells survive the radiation, the dimers were still associates with the large polynucleotides even after 48 hr of postirradiation incubation.