Comparison of AluI-induced frequencies of dicentrics and translocations inhuman lymphocytes by chromosome painting

It has been shown repeatedly that following irradiation of human lymphocyte s in the Go stage, more translocations are induced than dicentrics. To chec k the role of DNA double-strand breaks (DSB) alone for the induction of sym metrical and asymmetrical chromosome aberrations, the frequencies of induce d exchange aberrations by the restriction enzyme AluI were analyzed. The en zyme was introduced into cells using the pellet pipetting technique. Freque ncies of induced translocations and dicentrics were determined using a chro mosome painting assay with chromosome-specific DNA libraries for chromosome s 1, 4 and X (representing 16.8% of the human genome). The number of transl ocations detected was similar to 3-fold higher than the number of dicentric s, indicating that the increased frequency of translocations compared with dicentrics found in irradiated human lymphocytes does not result from DNA l esions other than DSB but from differential processing of DSB.