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M R Mattern

Publications and source records attributed to M R Mattern.

64 records · Page 4Linked to original sources
PubMed1979

Dependence of mammalian DNA replication on DNA supercoiling. I. Effects of ethidium bromide on DNA synthesis in permeable Chinese hamster ovary cells.

Chinese hamster ovary cells labelled with [14C]thymidine were made permeable, incubated with various concentrations of the intercalating dye ethidium bromide, and centrifuged through neutral sucrose gradients. The gradient profiles of these cells were qualitatively similar to those obtained by centrifuging DNA from untreated, lysed permeable cells through gradients containing ethidium bromide. The sedimentation distance of DNA had a biphasic dependence on the concentration of ethidium bromide, suggesting that the dye altered the amount of DNA supercoiling in situ. The effect of ethidium bromide intercalation on incorporation of [3H]dTMP into acid-precipitable material in an in vitro DNA synthesis mixture was measured. The incorporation of [3H]dTMP was unaffected by less than 1 microgram/ml of ethidium bromide, enhanced up to two-fold by 1--10 microgram/ml, and inhibited by concentrations greater than 10 micrograms/ml. Alkaline sucrose gradient analysis revealed a higher percentage of small DNA fragments (6--20 S) in the cells treated with 2 micrograms/ml ethidium bromide than in control cells. These fragments attained parental size within the same time as the fragments in control cells. In cells treated with 2 micrograms/ml ethidium bromide, a significant fraction of newly synthesized DNA resulted from new starts, whereas in untreated cells practically none of the newly synthesized DNA resulted from new starts. These results suggest that relaxation of DNA supercoiled structures ahead of the replication fork generates spurious initiations of DNA synthesis and that in intact cells the rate of chain elongation is limited by supercoiled regions ahead of the growing point.

Animals↗
PubMed1979

Dependence of mammalian DNA replication on DNA supercoiling. II. Effects of novobiocin on DNA synthesis in Chinese hamster ovary cells.

Novobiocin, an inhibitor of gyrase-induced DNA supercoiling and DNA replication in prokaryotes, inhibited the incorporation of DNA precursors into DNA in both intact and permeable Chinese hamster ovary cells; much higher concentrations were required for permeable cells, in which no new replicons were initiated. Nucleoids were prepared from cells that were incubated for 60 min with 200 micrograms/ml novobiocin, made permeable, and incubated with 0--50 micrograms/ml ethidium bromide. Sedimentation of the nucleoids in neutral sucrose gradients suggested that the number of supercoils in the average nucleoid had been reduced by prior incubation with novobiocin. In intact cells, novobiocin is required inside the cell for continued inhibition of DNA synthesis, suggesting that it does not act directly on the DNA. Alkaline sucrose gradient profiles of DNA synthesized in the presence of novobiocin in intact cells indicated that the drug inhibited replicon initiation while having little if any effect on chain elongation. These data are consistent with the idea that an activity similar to the bacterial gyrase generates supercoils in mammalian DNA and produces the proper conformation for the initiation of DNA replication.

Animals↗
PubMed1977

The organization of repeated nucleotide sequences in the replicons of mammalian DNA.

Chinese hamster ovary cells were irradiated with 100-5,000 rads of X-rays and inhibition of the initiation of replicons after irradiation was demonstrated by analyzing nascent DNA sedimented in alkaline sucrose gradients. The renaturation kinetics of DNA synthesized during 60 min of incubation after irradiation was compared with that of DNA synthesized during the 60 min after sham irradiation and with that of parental DNA. Nascent DNA from cells whose replicon initiation was inhibited renatured faster than nascent DNA from control cells in the COt range of repeated nucleotide sequences, suggesting that regions of the replicon not close to origins are enriched in repeated sequences and that regions close to origins are enriched in unique sequences. A class of repeated nucleotide sequences may be involved in the regulation of replicon initiation.

Base Sequence↗
PubMed1975

Selective excision of gamma ray damaged thymine from the DNA of cultured mammalian cells.

Three mammalian cell lines (WI-38, SV40-transformed WI-38 and Chinese hamster ovary) were exposed to high doses of 137-Cs gamma rays and their DNA analysed, following various periods of postirradiation incubation, for products of the 5,6-dihydroxy-dihydrothymine type. Within fifteen minutes of incubation at 37 degrees C 70 to 90 percent of these radiation products were removed from acid-precipitable material in all three cell lines. The amount of DNA degradation induced by radiation varied from approximately one percent in WI-38 cells to 15 percent in SV40-transformed WI-38 cells. Comparison of DNA degradation with the amount of thymine radiation product removed indicates that a selective gamma ray-induced excision repair capability exists in mammalian cells. Because of its more rapid kinetics, gamma ray excision repair is probably a distinct process as compared with ultraviolet-induced pyrimidine dimer excision.

Animals↗
PubMedDate not supplied

DNA-repair deficiencies do not affect intercalator-induced cytotoxicity or DNA scission in human cells.

The ability of the DNA intercalator m-AMSA to produce protein-associated DNA-strand breaks in normal, xeroderma pigmentosum and ataxia-telangiectasia fibroblasts was compared with m-AMSA uptake and cytotoxicity. No differences were detected between the cytotoxicity and DNA breakage produced by this antineoplastic acridine derivative among these three human cell lines. Uptake studies confirmed that no actual increased sensitivity was being masked by decreased intracellular drug. m-AMSA appears to be unique in its ability to produce breaks in cellular DNA that are not associated with an enhanced sensitivity in repair-deficient cells. Intercalator-induced, protein-associated DNA breaks are probably the result of a novel cellular response which differs from that which is abnormal in xeroderma pigmentosum or ataxia-telangiectasia cells.

Aminoacridines↗