Heterochromatin protein 1 binds to nucleosomes and DNA in Vitro

Heterochromatin protein 1 (HP1) is a nonhistone chromosomal protein primari ly associated with the pericentric heterochromatin and telomeres in Drosoph ila, The molecular mechanism by which HP1 specifically recognizes and binds to chromatin is unknown. The purpose of this study was to test whether HP1 can bind directly to nucleosomes. HP1 binds nucleosome core particles and naked DNA. HP1-DNA complex formation is length-dependent and cooperative bu t relatively sequence-independent. We show that histone H4 aminoterminal pe ptides bind to monomeric and dimeric HP1 in vitro. Acetylation of lysine re sidues had no significant effect on in vitro binding. The C-terminal chrome shadow domain of HPI specifically binds H4 N-terminal peptide. Neither the chrome domain nor chrome shadow domain alone binds DNA; intact native HP1 is required for such interactions. Together, these observations suggest tha t HP1 may serve as a cross-linker in chromatin, linking nucleosomal DNA and nonhistone protein complexes to form higher order chromatin structures.