Comparison of the folding of beta-globin and ovalbumin gene containing chromatin isolated from chicken oviduct and erythrocytes.

The dependence of chromatin conformation upon salt concentration has been studied for chicken ovalbumin and beta-globin genes isolated from oviduct and adult erythrocytes. At NaCl concentrations of 25 or 50 mM, the sedimentation properties, as a function of DNA size, of ovalbumin and globin chromatin are similar regardless of the source of the chromatin. In 100 mM NaCl, however, beta-globin chromatin isolated from erythrocytes sediments more slowly than an ovalbumin chromatin fraction from erythrocytes containing DNA of the same size. When the same experiment is carried out with material isolated from oviduct nuclei, the relative sedimentation rates are reversed, so that the ovalbumin chromatin sediments more slowly. This behavior cannot be accounted for by differences in binding of RNA polymerase or other molecules associated with transcription, or by partial aggregation of the chromatin. The most reasonable explanation is that transcriptionally active chromatin with a history of transcriptional activity, although largely covered with histones and capable of considerable compaction, is not able to form a fully compact structure as the ionic strength is raised. This behavior is consistent with a slight depletion in active chromatin of core histones or histone H1/H5 or both.