Induction of chromosome aberrations in unirradiated chromatin after partial irradiation of a cell nucleus

Purpose: It is generally accepted that chromosome exchanges in irradiated cells the formed through interactions between separate DNA doable-strand breaks (DSB). Here we tested whether non-irradiated DNA participate; in the formation of chromosome aberrations wen complex DNA DSB are induced elsewhere in the nucleus. Materials acid methods: Synchronized Chinese hamster cells containing an X chromosome with a late replicating q arm (X-q domain) were labelled with I-125-iododeoxyuridine ((125)IdUrd) in a period of S-phase when the vast majority of the X-q domain was not replicating. DNA damage froth I-125 decay as accumulated at the G1/S border while the culls were stored in liquid nitrogen. Decay of I-125 induced DSB in the immediate vicinity of the I-125 atom. Chromosome aberrations involving what is essentially the I-125-free X-q domain were scored at the first mitosis after cell thawing. As a positive control, cells were treated with (125)IdUrd at a later period in S-phase when the X-q domain replicates yielding a labelled X-q domain. Results: The I-125-free X-q domain exhibited chromosome aberrations (exchanges and fragments). The frequency of these aberrations seas linearly dependent on the number of I-125 decays elsewhere in the cell nucleus. The efficiency of formation of chromosome aberration by the I-125-free X-q domain teas approximately half of that observed in the I-125-labelled X-q domain. Conclusions: The involvement of the I-125-free X-q domain in chromosome aberration, suggests that DNA trot damaged by the decay of incorporated I-125 can interact with damaged DNA, indicating the existence of an alternative pathway fist, the formation of chromosome aberrations