Continuous and widespread roles for the Swi-Snf complex in transcription.

Chromatin presents a significant obstacle to transcription, but two means of overcoming its repressive effects, histone acetylation and the activities of the Swi-Snf complex, have been proposed. Histone acetylation and Swi-Snf activity have been shown to be crucial for transcriptional induction and to facilitate binding of transcription factors to DNA. By regulating the activity of the Swi-Snf complex in vivo, we found that active transcription requires continuous Swi-Snf function, demonstrating a role for this complex beyond the induction of transcription. Despite the presumably generalized packaging of genes into chromatin, previous studies have indicated that the transcriptional requirements for the histone acetyltransferase, Gcn5, and the Swi-Snf complex are limited to a handful of genes. However, inactivating Swi-Snf function in cells also lacking GCN5 revealed defects in transcription of several genes previously thought to be SWI-SNF- and GCN5-independent. These findings suggest that chromatin remodeling plays a widespread role in gene expression and that these two chromatin remodeling activities perform independent and overlapping functions during transcriptional activation.