The influence of growth medium on the yield of X-ray-induced chromatid exchanges in the presence and absence of aphidicolin

Time sequence of events leading to chromosomal aberration formation

Investigations have been carried out which have measured the influence of the repair polymerases on the yield of different types of chromosomal aberrations. The studies were mainly concerned with the effect of inhibiting the polymerases on the yield of aberrations. The polymerases fill in single strand regions, and the fact that their inhibition affects the yield of aberrations suggests that single strand lesions are influential in aberration formation. The results indicate that-- 1. There are two actions of polymerases in clastogenesis. One is in their involvement in a G2 repair system, in which the pair of chromatids is concerned, and which does not yield aberrations unless the inhibition is still operating when the cells enter mitosis. The second also operates in G1 and S, and is such that when repair is inhibited, further damage accrues. 2. The second action is affected by inhibiting polymerase but operates even when the repair enzymes are active. 3. The production of chromosomal exchanges involves a series of reactions, some of which are reversible. 4. The time span over which the reactions occur is much longer than has been envisaged previously (e.g., most of a cell cycle).