The SWI-SNF complex is involved in the activation of transcription via the remodeling of nucleosome structure in an ATP-dependent manner. Brm (also designated SNF2α) and Brg-1 (also designated SNF2β) are the ATPase subunits of the mammalian SWI/SNF complex. Brm, Brg-1, Ini1 (integrase interactor 1, also designated SNF5), BAF155 (also designated SRG3), and BAF170 are thought to comprise the functional core of the SWI/SNF complex. The addition of Ini1, BAF155, and BAF170 to Brg-1 appears to increase remodeling activity. Other complex subunits are thought to play regulatory roles. hSNF2L and hSNF2H both appear to be homologs of Drosophila ISWI, a Brm related ATPase that is present in chromatin remodeling complexes other than SWI/ SNF, including the NURF (nucleosome remodeling factor). BRG1 is mutated in multiple human tumors, including the hypercalcemic type of small cell carcinoma of the ovary and uterine sarcoma and undifferentiated carcinoma.