CHD1 IS CONCENTRATED IN INTERBANDS AND PUFFED REGIONS OF DROSOPHILA POLYTENE CHROMOSOMES

Previously, we reported on the discovery and characterization of a mam malian chromatin-associated protein, CHD1 (chromo-ATPase/helicase-DNA- binding domain), with features that led us to suspect that it might ha ve an important role in the modification of chromatin structure. We no w report on the characterization of the Drosophila melanogaster CHD1 h omologue (dCHD1) and its localization on polytene chromosomes. A set o f overlapping cDNAs encodes an 1883-aa open reading frame that is 50% identical and 68% similar to the mouse CHD1 sequence, including conser vation 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 pro teins, certain distinctive features of the CHD1 chrome and ATPase/heli case domains were revealed. The dCHD1 gene was mapped to position 23C- 24A on chromosome 2L. Western blot analyses with antibodies raised aga inst a dCHD1 fusion protein specifically recognized a approximate to 2 10-kDa protein in nuclear extracts from Drosophila embryos and culture d cells. Most interestingly, these antibodies revealed that dCHD1 loca lizes to sites of extended chromatin (interbands) and regions associat ed with high transcriptional activity (puffs) on polytene chromosomes from salivary glands of third instar larvae. These observations strong ly support the idea that CHD1 functions to alter chromatin structure i n a way that facilitates gene expression.