CHD1 is concentrated in interbands and puffed regions of Drosophila polytene chromosomes

Previously, we reported on the discovery and characterization of a mammalian chromatin-associated protein, CHD1 (chromo-ATPase/helicase-DNA-binding domain), with features that led us to suspect that it might have an important role in the modification of chromatin structure. We now report on the characterization of the Drosophila melanogaster CHD1 homologue (dCHD1) and its localization on polytene chromosomes. A set of overlapping cDNAs encodes an 1883-aa open reading frame that is 50% identical and 68% similar to the mouse CHD1 sequence, including conservation of the three signature domains for which the protein was named. When the chrome and ATPase/helicase domain sequences in various CHD1 homologues were compared with the corresponding sequences in other proteins, certain distinctive features of the CHD1 chrome and ATPase/helicase domains were revealed. The dCHD1 gene was mapped to position 23C-24A on chromosome 2L. Western blot analyses with antibodies raised against a dCHD1 fusion protein specifically recognized a approximate to 210-kDa protein in nuclear extracts from Drosophila embryos and cultured cells. Most interestingly, these antibodies revealed that dCHD1 localizes to sites of extended chromatin (interbands) and regions associated with high transcriptional activity (puffs) on polytene chromosomes from salivary glands of third instar larvae. These observations strongly support the idea that CHD1 functions to alter chromatin structure in a way that facilitates gene expression.