The human SWI/SNF-B chromatin-remodeling complex is related to yeast Rsc and localizes at kinetochores of mitotic chromosomes

The SWI/SNF family of chromatin-remodeling complexes facilitates gene expre ssion by helping transcription factors gain access to their targets in chro matin. SWI/SNF and Rsc are distinctive members of this family from yeast. T hey have similar protein components and catalytic activities but differ in biological function. Rsc is required for cell cycle progression through mit osis, whereas SWI/ SNF is not, Human complexes of this family have also bee n identified, which have often been considered related to yeast SWI/SNF. Ho wever, all human subunits identified to date are equally similar to compone nts of both SWI/SNF and Rsc, leaving open the possibility that some or all of the human complexes are rather related to Rsc, Here, we present evidence that the previously identified human SWI/SNF-B complex is indeed of the Rs c type. It contains six components conserved in both Rsc and SWI/SNF. Impor tantly, it has a unique subunit, BAF180, that harbors a distinctive set of structural motifs characteristic of three components of Rsc, Of the two mam malian ATPases known to be related to those in the yeast complexes, human S WI/SNF-B contains only the homolog that functions like Rsc during cell grow th. Immunofluorescence studies with a BAF180 antibody revealed that SWI/ SN F-B localizes at the kinetochores of chromosomes during mitosis, Our data s uggest that SWI/SNF-B and Rsc represent a novel subfamily of chromatin-remo deling complexes conserved from yeast to human, and could participate in ce ll division at kinetochores of mitotic chromosomes.