IDENTIFICATION AND CHARACTERIZATION OF DROSOPHILA RELATIVES OF THE YEAST TRANSCRIPTIONAL ACTIVATOR SNF2 SWI2/

The Drosophila brahma (brm) gene encodes an activator of homeotic gene s that is highly related to the yeast transcriptional activator SWI2 ( SNF2), a potential helicase. To determine whether brm is a functional homolog of SWI2 or merely a member of a family of SWI2-related genes, we searched for additional Drosophila genes related to SWI2 and examin ed their function in yeast cells. In addition to brm, we identified on e other Drosophila relative of SWI2: the closely related ISWI gene. Th e 1,027-residue ISWI protein contains the DNA-dependent ATPase domain characteristic of the SWI2 protein family but lacks the three other do mains common to brm and SWI2. In contrast, the ISWI protein is highly related (70% identical) to the human hSNF2L protein over its entire le ngth, suggesting that they may be functional homologs. The DNA-depende nt ATPase domains of brm and SWI2, but not ISWI, are functionally inte rchangeable; a chimeric SWI2-brm protein partially rescued the slow gr owth of swi2- cells and supported transcriptional activation mediated by the glucocorticoid receptor in vivo in yeast cells. These findings indicate that brm is the closest Drosophila relative of SWI2 and sugge st that brm and SWI2 play similar roles in transcriptional activation.