HMG-D and histone H1 alter the local accessibility of nucleosomal DNA

There is evidence that HMGB proteins facilitate, while linker histones inhibit chromatin remodelling, respectively. We have examined the effects of HMG-D and histone H1/H5 on accessibility of nucleosomal DNA. Using the 601.2 nucleosome positioning sequence designed by Widom and colleagues we assembled nucleosomes in vitro and probed DNA accessibility with restriction enzymes in the presence or absence of HMG-D and histone H1/H5. For HMG-D our results show increased digestion at two spatially adjacent sites, the dyad and one terminus of nucleosomal DNA. Elsewhere varying degrees of protection from digestion were observed. The C-terminal acidic tail of HMG-D is essential for this pattern of accessibility. Neither the HMG domain by itself nor in combination with the adjacent basic region is sufficient. Histone H1/H5 binding produces two sites of increased digestion on opposite faces of the nucleosome and decreased digestion at all other sites. Our results provide the first evidence of local changes in the accessibility of nucleosomal DNA upon separate interaction with two linker binding proteins.