ULTRASOFT 1.5-KEV ALUMINUM-K X-RAYS ARE EFFICIENT PRODUCERS OF COMPLEX CHROMOSOME EXCHANGE ABERRATIONS AS REVEALED BY FLUORESCENCE IN-SITU HYBRIDIZATION

The electron pairs generated by ultrasoft 1.5 keV aluminum K X-ray pho tons deposit their energy in tracks of length <70 nm and provide an id eal tool for analyzing the spatial distribution of breaks and misrepai r processes, We have undertaken the analysis of changes in chromosome structure produced by aluminum K X rays in untransformed HF12 human fi broblasts in G(1) phase using fluorescence in situ hybridization (FISH ). Multicolored chromosome-specific DNA probes for chromosomes 1 and 2 and an alpha-satellite pan-centromeric probe were used to examine in vitro radiation-induced chromosome-type exchange aberrations. After me an doses of 0.37-2.93 Gy the relative frequencies of complex exchanges , derived from three or more breaks in two or more chromosomes, ranged from 15-35%. For the classic breakage-and-rejoining theory to hold, v ery large interaction distances are needed to account for this high fr equency of multibreak interactions, unless many sites pre-exist where several different chromosomes come very close together. Alternatively, damaged DNA may be able to interact with adjacent undamaged DNA, obvi ating the need fdr large rejoining distances. (C) 1996 by Radiation Re search Society.