RADIATION-INDUCED CHROMOSOME-ABERRATIONS IN SACCHAROMYCES-CEREVISIAE - INFLUENCE OF DNA-REPAIR PATHWAYS

Radiation-induced chromosome aberrations, particularly exchange-type a berrations, are thought to result from misrepair of DNA double-strand breaks. The relationship between individual pathways of break repair a nd aberration formation is not clear. By electrophoretic karyotyping o f single-cell clones derived from irradiated cells, we have analyzed t he induction of stable aberrations in haploid yeast cells mutated for the RAD52 gene, the RAD54 gene, the HDF1(=YKU70) gene, or combinations thereof. We found low and comparable frequencies of aberrational even ts in wildtype and hdf1 mutants, and assume that in these strains most of the survivors descended from cells that were in G(2) phase during irradiation and therefore able to repair breaks by homologous recombin ation between sister chromatids. In the rad52 and the rad54 strains, e nhanced formation of aberrations, mostly exchange-type aberrations, wa s detected, demonstrating the misrepair activity of a rejoining mechan ism other than homologous recombination. No aberration was found in th e rad52 hdf1 double mutant, and the frequency in the rad54 hdf1 mutant was very low. Hence, misrepair resulting in exchange-type aberrations depends largely on the presence of Hdf1, a component of the nonhomolo gous end-joining pathway in yeast.