Radioresistant DNA synthesis: an intrinsic feature of ataxia telangiectasia.

DNA synthesis in 6 ataxia telangiectasia (AT) cell strains was much more resistant to X-irradiation than was DNA synthesis in normal human diploid cells. 3 of the cell strains tested have been classified as proficient in repair replication. These data, along with those reported elsewhere, strongly suggest that radioresistant DNA synthesis is an intrinsic feature of this disease. The radioresistance of DNA synthesis in AT cells is primarily due to a reduced inhibition of replicon initiation compared to that occurring in normal cells, but DNA chain elongation is also more radioresistant in AT cells. The small inhibition of DNA synthesis that does occur in AT cells at doses up to 2000 rad is almost exclusively due to inhibition of replicon initiation, and not to inhibition of chain elongation, as would be expected from results with normal human cells or from previous studies with established cell lines.