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

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Abstract
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.