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We have tested human fetal fibroblasts for development associated changes in DNA repair by utilizing nucleoid sedimentation as an assay for excision repair. Among skin fibroblasts the rate of excision repair was significantly higher in non-fetal cells than in fibroblasts derived from an 8 week fetus; this was evident by a delay in both the relaxation and the restoration of DNA supercoiling in nucleoids after irradiation. Skin fibroblasts derived at 12 week gestation were more repair proficient than those derived at 8 week gestation. However, they exhibited a somewhat lower rate of repair than non-fetal cells. The same fetal and non-fetal cells were also tested for induction of the protease plasminogen activator (PA) after u.v. irradiation. Enhancement of PA was higher in skin fibroblasts derived at 8 week than in those derived at 12 week gestation and was absent in non-fetal skin fibroblasts. These results are consistent with our previous findings that in human cells u.v. light-induced PA synthesis is correlated with reduced DNA repair capacity. Excision repair and PA inducibility were found to depend on tissue of origin in addition to gestational stage, as shown for skin and lung fibroblasts from the same 12 week fetus. Lung compared to skin fibroblasts exhibited lower repair rates and produced higher levels of PA after irradiation. The sedimentation velocity of nucleoids, prepared from unirradiated fibroblasts, in neutral sucrose gradients with or without ethidium bromide, indicated the presence of DNA strand breaks in fetal cells. It is proposed that reduced DNA repair in fetal cells may result from alterations in DNA supercoiling, and that persistent DNA strand breaks enhance transcription of PA gene(s). [ABSTRACT FROM PUBLISHER]

Silver staining and polyacrylamide gel electrophoresis were used to visualize chain length distribution of poly(ADP-ribose) enzymatically synthesized from NAD by rat liver nuclei. The method described has the advantage that synthesis does not require radioactive-labeled NAD, and microgram quantities (greater than 5 micrograms) of poly(ADP-ribose) can be resolved and visualized as discrete bands according to chain lengths which range from 8 to 60 residues. This method can be applied to estimate size distribution of poly(ADP-ribose) chains in cells or tissues.

The correlation between 5-fluorouracil-induced resistance to ultraviolet (UV) light and the ability of bacterial cells to repair irradiation damage was investigated in various strains of Escherichia coli. Preincubation with 5-fluorouracil did not influence the dark-repair mechanism. It affected, however, the UV light-induced damage of cell division in filament-forming strains. It is suggested that the delay in postirradiation macromolecular synthesis of 5-fluorouracil-pretreated bacteria plays a decisive role in the recovery process leading to cross cell wall-forming ability in the damaged strains.

Ben-Ishai, Ruth (Israel Institute of Technology, Haifa), Michal Lahav, and Ada Zamir. Control of uracil synthesis by arginine in Escherichia coli. J. Bacteriol. 87:1436-1442. 1964.-It is shown that arginine affects uracil biosynthesis in Escherichia coli. The effect of arginine on uracil synthesis was analyzed by following the changes in the level of aspartate transcarbamylase, the first specific enzyme in uracil synthesis. In this research, an effect of arginine on aspartate transcarbamylase formation was observed only if the bacteria were preincubated with arginine in the presence of uracil analogues that cause apparent partial derepression of this enzyme. The possible effect of a structural modification of aspartate transcarbamylase by 2-thiouracil, the analogue principally used, is considered. However, it is shown that arginine causes derepression of aspartate transcarbamylase, even if a modification of the enzyme occurs. An effect of uracil on arginine synthesis can also be observed in repressible strains of E. coli, if conditions of partial derepression of the enzymes involved in arginine synthesis prevail. However, neither the derepression of aspartate transcarbamylase by arginine nor the derepression of ornithine transcarbamylase by uracil is accompanied by changes in the level of carbamyl phosphokinase, the enzyme that catalyzes carbamyl phosphate synthesis.