The rate of removal of pyrimidine dimers in quiescent cultures of normal human and xeroderma pigmentosum cells.
The rate of removal of pyrimidine dimers from DNA of UV (254 nm)-irradiated (1 J/m2) normal and xeroderma pigmentosum (XP) cells maintained in culture as nondividing populations was determined. Several normal and XP strains from complementation groups A, C and D were studied. The excision rates and survival ability of nondividing cells were examined to determine if an abnormal sensitivity was associated with a decreased rate of dimer excision. The results show that all normal strains studied excise pyrimidine dimers at the same rate, with the rate curve characterized by two components. All 'excision-deficient' XP strains excise dimers at a slower-than-normal rate, with the rate curves also characterized by two components. The rate constants for the first components of all of the XP strains (group A, C and D) are the same, one tenth of the normal rate constant, except for XP8LO (group A). XP8LO has a first-component rate constant similar to that of normal strains and a second component rate constant similar to that of other group A strains (XP12BE, XP25RO). Thus, the slower rate of dimer excision in XP8LO is due to a defect in the mechanism responsible for the second component of the excision-rate curve. In general, an abnormal sensitivity of nondividing cells to UV is associated with a reduced dimer-excision rate. A notable exception to this is the group C strain XP1BE which has an initial repair rate similar to that of group A XP12BE but is considerably more resistant when survival is measured.
D002460:Cell Line; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007700:Kinetics; D011740:Pyrimidine Dimers / Q000528:radiation effects*; D012016:Reference Values; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000378:metabolism*
D011740:Pyrimidine Dimers