On the origin of chromosomal aberrations in human peripheral lymphocytes in vitro. I. Experiments with Neurospora endonuclease and polyethylene glycol.

Post-treatment of mutagen-treated human peripheral lymphocytes with a single-strand specific endonuclease from Neurospora crassa leads to a significant elevation of the rate of structural chromosomal aberrations. Our results indicate that DNA double-strand breaks (DSB) are ultimate lesions for the formation of chromosomal aberrations in the G1 and G2 phase of the cell cycle and probably also in the S-phase. Post-treatment of X-irradiated G2 cells with polyethylene glycol (PEG) leads to an elevation of the frequencies of chromatid type aberrations. This result is taken as an indication that nucleases from PEG-damaged lysosomes transform lesions in X-ray damaged chromosomes to DSB. With respect to the origin of chromosomal aberrations, our results are in favour of the breakage and reunion hypothesis of K. Sax , and not of Revell 's exchange hypothesis.