Differential nuclease sensitivity of the ovalbumin and β-globin chromatin regions in erythrocytes and oviduct cells of laying hen

We have monitored the differential nuclease sensitivity of defined regions of the chicken genome in different cells using a method which combines restriction enzyme digestion and blotting to dlazobenzyloxymethyl (DBM)-paper (see Ref. 11). By using different specific probes and by scanning the bands on the autoradiograms, it is possible to compare on the same blot the digestion patterns of similar-sized fragments from different regions of the genonie corresponding to "active" and reference "inactive" genes. We have demonstrated the preferential sensitivity to DNaseI and micrococcal nuclease digestion of the ovalbumin gene region in hen oviduct chromatin. The β-globin gene region (containing both an adult and an embryonic gene) is also preferentially digested by DNaseI in hen mature erythrocyte nuclei, but at a lower rate than the ovalbumin gene region in oviduct. These observations raise the possibility that there may be several types of preferential nuclease sensitivities, all characterized by increased rates of digestion but to different levels, the highest corresponding to the very actively transcribing genes.