Sensitivity of excision repair in normal human, xeroderma pigmentosum variant and Cockayne's syndrome fibroblasts to inhibition by cytosine arabinoside

Journal Article · Sat Aug 01 00:00:00 EDT 1981 · J. Cell. Physiol.; (United States)

DOI:https://doi.org/10.1002/jcp.1041080207· OSTI ID:6162446

Cleaver, J E

Inhibition of the gap-filling, polymerizing step of excision repair by 1-..beta..-D-arabinofuranosylcytosine (ara-C) after irradiation with ultraviolet light in human diploid fibroblasts resulted in the formation of persistent DNA strand breaks in G/sub 1/, G/sub 2/, and plateau phase cells, but not in S phase cells. Addition of hydroxyurea to ara-C resulted in partial inhibition of repair in S phase cells. These observations can be explained either in terms of changing roles in repair for different DNA polymerases throughout the cell cycle or by the presence of a pool of deoxycytidine nucleotides during S phase equivalent to an external source of deoxycytidine at 50 ..mu..M concentration. A similar concentration dependence on ara-C was observed for inhibition of repair in normal human, xeroderma pigmentosum (XP) variant, and Cockayne's syndrome cells. Ara-C produced a similar number of breaks in normal and Cockayne's syndrome cells. Ara-C produced a similar number of breaks in normal and Cockayne's syndrome cells but slightly more in XP variant cells. Exonuclease III and S1 nuclease independently both degraded about 50% of the /sup 3/H-thymidine incorporated into repaired regions in the presence of ara-C. Sequential digestion with both enzymes degraded nearly 90% of the repaired regions. These observations can be explained if excision repair proceeds by displacing the damaged strand so that both the /sup 3/H-labeled patch and the damaged region are still ligated to high molecular weight DNA and compete for the same complementary strand during in vitro incubation with the nucleases. The amount of /sup 3/H-thymidine incorporated in DNA by repair decreased with increasing concentrations of ara-C and hydroxyurea, suggesting that the incomplete patches became shorter under these conditions. Extrapolation of the digestion kinetics with exonuclease III permits an estimate of the normal patch size of about 100 nucleotides, consistent with previous estimates.

• Research Organization: Univ. of California, San Francisco
• OSTI ID: 6162446
• Journal Information: J. Cell. Physiol.; (United States), Vol. 108:2
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
59 BASIC BIOLOGICAL SCIENCES
CYTOSINE
GENETIC EFFECTS
FIBROBLASTS
SENSITIVITY
STRAND BREAKS
BIOLOGICAL REPAIR
XP CELLS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL PATHWAYS
CELL CYCLE
COMPARATIVE EVALUATIONS
DNA
ENZYME ACTIVITY
MUTATIONS
POLYMERASES
QUANTITY RATIO
THYMIDINE
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ULTRAVIOLET RADIATION
AMINES
ANIMAL CELLS
AZINES
BIOLOGICAL EFFECTS
BIOLOGICAL RECOVERY
CONNECTIVE TISSUE CELLS
ELECTROMAGNETIC RADIATION
ENZYMES
HETEROCYCLIC COMPOUNDS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
NUCLEIC ACIDS
NUCLEOSIDES
NUCLEOTIDES
NUCLEOTIDYLTRANSFERASES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOSPHORUS-GROUP TRANSFERASES
PYRIMIDINES
RADIATIONS
REACTION KINETICS
RECOVERY
REPAIR
RIBOSIDES
SOMATIC CELLS
TRANSFERASES
560121* - Radiation Effects on Cells- External Source- (-1987)
550301 - Cytology- Tracer Techniques
550401 - Genetics- Tracer Techniques
550201 - Biochemistry- Tracer Techniques