ABSTRACT
Single-strand breaks (SB) in DNA of irradiated thymocytes are first repaired, at a half-recovery period of a few minutes, then the number of breaks rapidly increases indicating that in addition to chromatin endonucleolysis there is an imbalance between the repair enzymes that generate DNA breaks and eliminate them. The rate of SB accumulation in thymocyte fractions, upon incubation of the cells with 1-beta-D-arabinofuranosyl cytosine (AraC) and hydroxyurea (HU), is directly proportional to their radiosensitivity, whereas DNA ligase activity is higher in a fraction of highly radioresistant thymocytes. Chemical compounds that increase the survival rate of irradiated thymocytes decelerate SB accumulation in DNA and sensitivity of cells to AraC and HU. Ineffective substances have no such an effect.
Subject(s)
DNA Damage , DNA Ligases/radiation effects , DNA, Single-Stranded/radiation effects , Polynucleotide Ligases/radiation effects , Radiation Tolerance , Thymus Gland/radiation effects , Animals , Cytarabine/pharmacology , DNA Repair/drug effects , DNA Repair/radiation effects , DNA, Single-Stranded/drug effects , Gamma Rays , Hydroxyurea/pharmacology , Kinetics , Male , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Thymus Gland/cytology , Thymus Gland/drug effects , Thymus Gland/enzymologySubject(s)
DNA Ligases/radiation effects , Escherichia coli/radiation effects , Polynucleotide Ligases/radiation effects , Pyrimidines/metabolism , DNA Ligases/metabolism , DNA, Bacterial/metabolism , Enzyme Activation/radiation effects , Escherichia coli/enzymology , Escherichia coli/metabolism , Gamma Rays , Light , Ultraviolet RaysABSTRACT
The DNA ligase activity of monkey kidney CV-1 cells has been measured at different stages of culture growth and after different time intervals following ultraviolet irradiation. Results indicate that: - The level of enzyme activity is about twice higher in non synchronous, rapidly dividing cells than in confluent cultures. - UV-irradiation of cells induces a "de novo" synthesis of DNA ligase. - This induction is dose dependent in its extent and kinetics, and may lead to a DNA ligase level in UV-irradiated stationary cultures of the same order as observed in unirradiated exponentially growing cells. - This induction seems to be independent of semiconservative DNA synthesis since it is not affected by fluorodeoxyuridine.
