KINETICS OF THE FORMATION OF CHROMOSOME-ABERRATIONS IN X-IRRADIATED HUMAN-LYMPHOCYTES - ANALYSIS BY PREMATURE CHROMOSOME CONDENSATION WITH DELAYED FUSION

Human lymphocytes irradiated with graded doses of up to 5 Gy of 150 kV X rays were fused with mitotic CHO cells after delay times ranging fr om 0 to 14 h after irradiation. The yields of dicentrics seen under PC C conditions, using C-banding for centromere detection, and of excess acentric fragments observed in the PCC experiment were determined by i mage analysis. At 4 Gy the time course of the yield of dicentrics show s an early plateau for delay times up to 2 h, then an S-shaped rise an d a final plateau which is reached after a delay time of about 8 to 10 h. Whereas the dose-yield curve measured at zero delay time is strict ly linear, the shape of the curve obtained for 8 h delay time is linea r-quadratic. The linear yield component, alpha D, is formed entirely i n the fast process manifested in the early plateau, while component be ta D-2 is developed slowly in the subsequent hours. Analysis of the ki netics of the rise of the S-shaped curve for yield as a function of ti me leads to the postulate of an ''intermediate product'' of pairwise D NA lesion interaction, Still fragile when subjected to the stress of P CC, but gradually processed into a stable dicentric chromosome. It is concluded that the observed difference in the kinetics of the alpha an d beta components explains a number of earlier results, especially the disappearance of the beta component at high LET, and opens possibilit ies for chemical and physical modification of the beta component durin g the extended formation process after irradiation observed here. (C) 1995 by Radiation Research Society