Evidence for Location of the Site of Accumulation for Sub-lethal Damage in Chlamydomonas

Summary

Small doses of ultraviolet light (254 nm) have been found to affect recovery of cells from sub-lethal ionizing radiation damage. When cells were exposed to U.V. light immediately before or after the first of two exposures to ionizing radiation and then held in the dark between the two radiation exposures, they showed a reduced capacity to recover from sub-lethal radiation damage. If cells were exposed to U.V. light before the first of two ionizing radiation doses and then photoreactivated between the two doses, full Elkind recovery was observed. Exposure of cells to a small U.V. dose did not reduce the width of the shoulder on the single-dose survival curve.

We conclude from these results that U.V. light damage in the form of pyrimidine dimers presents a block to the repair of cells damaged sub-lethally by ionizing radiation. This block can be removed by photoreactivation, which suggests that the site of accumulation and repair of sub-lethal radiation damage is in the DNA.