[The mechanism of radioresistant DNA synthesis in ataxia telangiectasia]

Using DNA fiber autoradiography, DNA replication in cells of healthy donors and in those of patients with ataxia telangiectasia (AT) was estimated. A new fact has been demonstrated showing a decreased number of simultaneously operating in tandem groups of replicon clusters in AT cells compared to that in normal cells. The data obtained suggest a reduced frequency of activation in the adjacent replicon clusters in AT cells. It should be noted that the rate of fork movement remained unchanged in AT cells. Besides, the frequency of replication in adjacent replicon clusters remained unaltered after 5 Gy irradiation in AT cells, while the normal cells were radiosensitive to reduction in this replication parameter to the low level seen in both non-irradiated and 5 Gy irradiated AT cells. The relation of the above data to radioresistant DNA synthesis is discussed.