Quantitation of DNase I sensitivity in Xenopus chromatin containing active and inactive globin, albumin and vitellogenin genes.

The disappearance of defined restriction fragments of the beta 1-globin, an albumin and the A1 vitellogenin gene was quantitated after DNase I digestion and expressed by a sensitivity factor defined by a mathematical model. Analysis of naked DNA showed that the gene fragments have similar but not identical sensitivity factors. DNase I digestion of chromatin revealed for the same gene fragments sensitivity factors differing over a much wilder range. This is correlated to the activity of the genes analyzed: the beta 1-globin gene fragment is more sensitive to DNase I in chromatin of erythrocytes compared to hepatocytes whereas the albumin gene fragment is more sensitive to DNase I in chromatin of hepatocytes. The A1 vitellogenin gene has the same DNase I sensitivity in both cell types. Comparing the DNase I sensitivity of the three genes in their inactive state we suggest that different chromatin conformations may exist for inactive genes.