DNA-BINDING AND CHROMATIN LOCALIZATION PROPERTIES OF CHD1

CHD1 is a novel DNA-binding protein that contains both a chromatin org anization modifier (chrome) domain and a helicase/ATPase domain. We sh ow here that CHD1 preferentially binds to relatively long A . T tracts in double-stranded DNA via minor-groove interactions. Several CHD1-bi nding sites were found in a well-characterized nuclear-matrix attachme nt region, which is located adjacent to the intronic enhancer of the k appa immunoglobulin gene. The DNA-binding activity of CHD1 was localiz ed to a 229-amino-acid segment in the C-terminal portion of the protei n, which contains sequence motifs that have previously been implicated in the minor-groove binding of other proteins. We also demonstrate th at CHD1 is a constituent of bulk chromatin and that it fan be extracte d from nuclei with 0.6 M NaCl or with 2 mM EDTA after mild digestion w ith micrococcal nuclease. In contrast to another chrome-domain protein , HP1, CHD1 is not preferentially located in condensed centromeric het erochromatin, even though centromeric DNA is highly enriched in (A+T)- rich tracts. Most interestingly, CHD1 is released into the cytoplasm w hen cells enter mitosis and is reincorporated into chromatin during te lophase-cytokinesis. These observations lend credence to the idea that CHD1, like other proteins with chrome or helicase/ATPase domains, pla ys an important role in the determination of chromatin architecture.