Selective solubilization of .beta.-globin oligonucleosomes at low ionic strength

We [Rocha, E., Davie, J.R., van Holde, K.E., & Weintraub, H. (1984) J. Biol. Chem. 259, 8558-8563] have previously reported that the transcriptionally competent beta-globin gene domain is selectively enriched in chromatin fractions eluted with solutions of approximately physiological ionic strength from micrococcal nuclease digested mature chicken erythrocyte nuclei. In this report, we demonstrate that beta-globin chromatin is eluted as oligonucleosomes while vitellogenin, a transcriptionally inactive gene, is eluted as mononucleosomes as is the bulk of sequences found in this fraction. Following removal of the salt, the eluted chromatin was made 100 mM KCl and separated into aggregation-prone and aggregation-resistant fractions. Globin sequences were present in both fractions and had the greatest enrichment in the aggregation-prone fraction which contained H1 and H5, H1 being more abundant. A procedure is presented in which H1 is selectively removed from the erythrocyte nuclei. Following the selective removal of H1 and subsequent fractionation, globin but not vitellogenin oligonucleosomes were present in the aggregation-resistant chromatin fraction. The results indicate the beta-globin domain is a mosaic of aggregation-resistant and aggregation-prone regions with the latter being associated with H1 and H5. Vitellogenin sequences were associated principally with aggregation-prone regions complexed with H5.