Probing the free space within rat and chicken chromatin with active and passive probes

The cavity systems within chicken erythrocyte nuclei and rat liver nuclei were compared using passive probes of radioactive glycogen and active probes of nuclease-armed-glycogen. The passive probe curves have a form that indicates that they are due to passive occupation of spaces and not due to the effects of a limiting membrane. The technique of probing nuclei with glycogen armed with a small enzyme is described. The chicken erythrocytes appeared to have 11–15-nm and 4–5-nm cacity systems similar to those we have previously reported in rat nuclei. Evidence is presented to show that the bridge DNA is enclosed within the 4–5 nm cavities in both rat liver and chicken erythrocyte nuclei. Minor differences between the rat liver and chicken erythrocyte nuclear cavity systems are noted in the region of 5–8 nm. A relatively mild procedure is described for preparing chicken erythrocyte nuclei.