A lysine-rich protein functions as an H1 histone in Dictyostelium discoideum chromatin

摘要

Mononucleosomes released from Dictyostelium discoideum chromatin by micrococcal nuclease contained two distinctive DNA sizes (166–180 and 146 bp). Two dimensional gel electrophoresis suggested a lysinerich protein protected the larger mononucleosomes from nuclease digestion. This was confirmed by stripping the protein from chromatin with Dowex resin. Subsequently, only the 146 bp mononucleosome was produced by riuclease digestion. Reconstitution of the stripped chromatin with the purified lysine-rich protein resulted in the reappearance of the larger inononucleosomes. Two-dimensional gel electrophoresis showed the protein was associated with mononucleosomes. Hence, the protein functions as an Hl histone in bringing the two DNA strands together at their exit point from the nucleosome. Trypsin digestion of the lysinerich protein in nuclei resulted in a limiting peptide of approx. 10 kilodaltons. Trypsin concentrations which degraded the protein to peptides of 12–14 kilodaltons and partially degraded the core histones did not change the DNA digestion patterns obtained with micrococcal nuclease. Thus, the trypsin-resistant domain of the lysine-rich protein is able to maintain chromatosome structure.