Comparison of susceptibility to staphylococcal nuclease and behaviour in metrizamide gradients of normal and 5-bromodeoxyuridine-substituted chromatin from Physarum polycephalum.

Replacement of 20--30% of thymine by 5-bromodeoxyuridine in chromatin DNA of Physarum polycephalum does not cause any visible change in a typical, regular pattern of DNA products obtained upon digestion of chromatin with staphylococcal nuclease. The time course of digestion is similar for normal and substituted chromatin even under conditions when the nuclease cleaves preferentially the dAT regions in DNA. 5-Bromodeoxyuridine label does not significantly affect the DNA/protein ratio in chromatin; this is reflected by similar behaviour of normal and substituted chromatin in metrizamide-density gradients.