Essential roles of Snf5p in Snf-Swi chromatin remodeling in vivo.

Snf-Swi, the prototypical ATP-dependent nucleosome-remodeling complex, regulates transcription of a subset of yeast genes. With the exception of Snf2p, the ATPase subunit, the functions of the other components are unknown. We have investigated the role of the conserved Snf-Swi core subunit Snf5p through characterization of two conditional snf5 mutants. The mutants contain single amino acid alterations of invariant or conserved residues that abolish Snf-Swi-dependent transcription by distinct mechanisms. One mutation impairs Snf-Swi assembly and, consequently, its stable association with a target promoter. The other blocks a postrecruitment catalytic remodeling step. These findings suggest that Snf5p coordinates the assembly and nucleosome-remodeling activities of Snf-Swi.