Abstract
The digestion by DNAase I of DNA synthesised by isolated chicken erythroblasts was examined in isolated nuclei. It was found that newly synthesised DNA was susceptible to DNAase I but matured to a relatively resistant form with increasing time after replication as observed in mammalian systemsll,12. The presence of trypsin in the digestion exposed all of the DNA to DNAase I action. Examination of the digestion products showed that the newly replicated DNA differed little from the more mature form in the structure of the DNA-protein complex but that the difference in susceptibility was probably a result of a differential rate of access of the DNAase to the new and old DNA.