Osa associates with the Brahma chromatin remodeling complex and promotes the activation of some target genes

The yeast SWI/SNF complex and its Drosophila and mammalian homologs are tho ught to control gene expression by altering chromatin structure, but the me chanism and specificity of this process are not fully understood. The Droso phila osa gene, like yeast SWI1, encodes an AT-rich interaction (ARID) doma in protein. We present genetic and biochemical evidence that Osa is a compo nent of the Brahma complex, the Drosophila homolog of SWI/SNF. The ARID dom ain of Osa binds DNA without sequence specificity in vitro, but it is suffi cient to direct transcriptional regulatory domains to specific target genes in vivo. Endogenous Osa appears to promote the activation of some of these genes. We show evidence that some Brahma-containing complexes do not conta in Osa and that Osa is not required to localize Brahma to chromatin. These data suggest that Osa modulates the function of the Brahma complex.