REARRANGEMENT OF THE HISTONE H2A C-TERMINAL DOMAIN IN THE NUCLEOSOME

Using zero-length covalent protein-DNA crosslinking, we have mapped th e histone-DNA contacts in nucleosome core particles from which the C- and N-terminal domains of histone H2A were selectively trimmed by tryp sin or clostripain. We found that the flexible trypsin-sensitive C-ter minal domain of histone H2A contacts the dyad axis, whereas its globul ar domain contacts the end of DNA in the nucleosome core particle. The appearance of the histone H2A contact at the dyad axis occurs only in the absence of linker DNA and does not depend on the absence of linke r histones. Our results show the ability of the histone H2A C-terminal domain to rearrange. This rearrangement might play a biological role in nucleosome disassembly and reassembly and the retention of the H2A- H2B diner (or the whole octamer) during the passing of polymerases thr ough the nucleosome.