Enhanced phosphorylation of high-mobility-group proteins in nuclease-sensitive mononucleosomes from butyrate-treated HeLa cells.

The protein composition of nucleosome fractions differing in their sensitivity to micrococcal nuclease and derived from butyrate-treated or untreated HeLa cells has been compared. Most of the high-mobility-group-14 (HMG-14) and HMG-17 content of HeLa cell chromatin is associated with those nucleosomes that are preferentially sensitive to micrococcal nuclease. Furthermore, electrophoresis of these two HMG proteins from the transcriptionally active chromatin fraction MN1 of butyrate-treated cells resolves them into a series of bands. The multiple band pattern of HMG-14 and -17 from butyrate-treated cells results from hyperphosphorylation rather than hyperacetylation. Phosphorylation of these two small nonhistone proteins may play some role in the modulation of the structure of transcriptionally active chromatin.