A general method for purification of H1 histones that are active for repression of basal RNA polymerase II transcription.

H1 histones were purified from extracts of salt-treated nuclei as a co-product of RNA polymerase II transcription factors from both Drosophila embryos and HeLa cells by a simple and general method. This procedure was also used to purify H1 as co-product of the core histones from calf thymus. The key steps in this purification exploit the solubility of H1 in 2.26 M ammonium sulfate and the chromatographic properties of the highly charged H1 molecules on a phenyl-Sepharose resin. H1 that is prepared by this procedure is active for in vitro repression of basal RNA polymerase II transcription. This method provides a new means of purifying H1 by a mild procedure that is likely to be generally useful for studies of transcription and chromatin structure.