After chromatin is SWItched-on can it be RUSHed?

Repressive chromatin must be remodeled to allow for transcriptional activat ion of genes in eukaryotic cells. Factors that alter chromatin structure to permit access of transcriptional activators, RNA polymerase II and the pol ymerase-associated general transcription factors to nucleosomal promoter se quences are as highly conserved as the basic mechanism of transcription. On e group of promoter restructuring factors that perturbs chromatin in an ATP -dependent manner includes NURF, CHRAC, ACF, the SWI/SNF complex, and SWI/S NF-related proteins. Each member of this group contains a subunit homologou s to the DNA-dependent ATPase; however, their individual mechanisms of acti on are unique. The small amount of SWI/SNF complex (100-200 copies/cell), i ts affiliation with a select number of inducible genes, and its interaction with the glucocorticoid and estrogen receptors, suggests the SWI/SNF compl ex might be preferentially targeted to active promoters. The SWI/SNF-relate d family of RUSH proteins which includes RUSH-1 alpha and beta, hHLTF, HIP1 16, Zbu1, P113, and the transcription factor RUSH-la isolog has been implic ated as a highly conserved DNA binding site-specific ATPase. (C) 1999 Elsev ier Science Ireland Ltd. All rights reserved.