Antagonistic remodelling by Swi-Snf and Tup1-Ssn6 of an extensive chromatin region forms the background for FLO1 gene regulation.

Novel yeast histone mutations that confer Swi-Snf independence (Sin(-)) were used to investigate the mechanisms by which transcription coactivator complexes relieve chromatin repression in vivo. Derepression of the flocculation gene FLO1, which is normally repressed by the Tup1-Ssn6 corepressor, leads to its identification as a constitutive Swi-Snf-dependent gene. We demonstrate that Tup1-Ssn6 is a chromatin remodelling complex that rearranges and also orders nucleosomal arrays on the promoter and over 5 kb of upstream intergenic region. Our results confirm that the Swi-Snf complex disrupts nucleosome positioning on promoters, but reveal that it can also rearrange nucleosomes several kilobases upstream from the transcription start site. The antagonistic chromatin remodelling activities of Swi-Snf and Tup1-Ssn6 detected in an array of 32 nucleosomes upstream of FLO1 extend far beyond the scale of promoter-based models of chromatin-mediated gene regulation. The Swi-Snf coactivator and Tup1-Ssn6 corepressor control an extensive chromatin domain in which regulation of the FLO1 gene takes place.