MICROPHOTOMETRIC SCANNING OF CHROMATID GAPS AND BREAKS INDUCED BY ALUI AND BAMHI IN CHINESE-HAMSTER OVARY CELLS

Chromatid gaps and breaks induced by the restriction endonucleases Alu I and BamHI in the long arm of chromosome 1 of Chinese hamster ovary c ells were microphotometrically scanned and mapped to a quantitative G- band map. More than 50% of chromatid breaks appeared as chromatin loss es of greater than 5% of the total arm length. The majority of chromat id gaps and breaks as well as chromatin losses induced by both restric tion endonucleases were non-randomly located in a region from 0.35 to 0.65 relative length units of the long arm of chromosome 1. We suggest that the access of these endonucleases to chromosomal DNA depends on the local organization of the chromatin.