Expanding the Mot1 subfamily: 89B helicase encodes a new Drosophila melanogaster SNF2-related protein which binds to multiple sites on polytene chromosomes.

Many proteins of the SNF2 family, which share a similar DNA-dependent ATPase/putative helicase domain, are involved in global transcriptional control and processing of DNA damage. We report here the partial cloning and characterization of 89B helicase, a gene encoding a new Drosophila melanogaster member of the SNF2 family. 89B Helicase protein shows a high degree of homology in its ATPase/helicase domain to the global transcriptional activators SNF2 and Brahma and to the DNA repair proteins ERCC6 and RAD54. It is, however, most strikingly similar to the Saccharomyces cerevisiae protein Mot1, a transcriptional repressor with many target genes for which no homologue has yet been described. 89B helicase is expressed throughout fly development and its large transcript encodes a >200 kDa protein. Staining with anti-89B Helicase antibodies reveals that the protein is present uniformly in early embryos and then becomes localized to the ventral nerve cord and brain. On the polytene chromosomes, 89B Helicase is bound to several hundred specific sites that are randomly distributed. The homology of 89B Helicase to Mot1, its widespread developmental expression and its large number of targets on the polytene chromosomes of larval salivary gland cells suggest that 89B Helicase may play a role in chromosomal metabolism, particularly global transcriptional regulation.