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 transcriptiona l control and processing of DNA damage, We report here the partial clo ning and characterization of 89B helicase, a gene encoding a new Droso phila melanogaster member of the SNF2 family. 89B Helicase protein sho ws a high degree of homology in its ATPase/helicase domain to the glob al transcriptional activators SNF2 and Brahma and to the DNA repair pr oteins ERCC6 and RAD54. It is, however, most strikingly similar to the Saccharomyces cerevisiae protein Mot1, a transcriptional repressor wi th many target genes for which no homologue has yet been described, 89 B helicase is expressed throughout fly development and its large trans cript encodes a >200 kDa protein, Staining with anti-89B Helicase anti bodies 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 specif ic sites that are randomly distributed, The homology of 89B Helicase t o Mot1, its widespread developmental expression and its large number o f targets on the polytene chromosomes of larval salivary gland cells s uggest that 89B Helicase may play a role in chromosomal metabolism, pa rticularly global transcriptional regulation.