INFLUENCE OF ARA-A ON THE FORMATION OF DICENTRICS IN IRRADIATED QUIESCENT CHO CELLS

CHO K1-cells, arrested in G(0)/G(1) phase were irradiated with graded doses of 150-kV X-rays, and the dicentric chromosome aberrations in th e first metaphase after reincubation in full growth medium were evalua ted. When 500 mu M ara A was administered at least 1 h before irradiat ion, maximal enhancement of the dicentric yield was obtained under 'im mediate plating' conditions as well as under 'delayed plating' conditi ons, and under both conditions only the linear component alpha D of th e aberration yield was affected. Since ara A had no effect upon the nu mber of induced dsbs, as measured with PFGE at doses up to 100 Gy, the action pathway of ara A is suggested to be the repair/misrepair proce ss manifested in the linear component of the dicentric yield. By varyi ng the time at which either ara A at 37 degrees C was administered bef ore irradiation or ara A at 4 degrees C was added after irradiation, i t was observed that the repair step sensitive to ara A was completed w ithin about 5 min after irradiation. This is in agreement with other o bservations of ara A action upon a fast repair step. The conversion of DNA single-strand breaks or base damage sites into double-strand brea ks as a consequence of polymerase beta inhibition by ara A would expla in the present results.