Kinetics of nuclease digestion of Physarum polycephalum nuclei at different stages of the cell cycle

The kinetics of nuclease digestion of Physarun polycephalum nuclei by staphylococcal nuclease and DNase I has been studied at different stages of the cell cycle. Significant differences in the digestion behaviour of nuclei from metaphase and interphase have been detected with DNase I but not with staphylococcal nuclease. Furthermore the structure of newly replicated DNA in S phase differs from the bulk in that it is more easily degraded to acid‐soluble products by either staphylococcal nuclease or by DNAse I. At least four types of chromatin structure can be distinguished by our digestion kinetics experiments.