Restriction endonuclease Bam H I induces chromosomal aberrations in Chinese hamster ovary (CHO) cells

Treatment of Chinese hamster ovary (CHO) cells with the restriction endonuclease Bam H I (recognition site: G/GATCC) leads to high frequencies of chromosomal aberrations. Experiments with bromodeoxyuridine-labelled chromosomes show that the aberrations occur nearly exclusively in first post-treatment metaphases. The results are interpreted to mean that only some of the cells take up the enzyme and that these cells are the ones showing the aberrations. Cells which do not take up the enzyme show up as differentially stained metaphases and have no aberrations. Why some cells take up the restriction enzyme and others not is not known, possibly this is dependent on the physiological condition of the cells.