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(-)) wer e used to investigate the mechanisms by which transcription coactivator com plexes relieve chromatin repression in vivo. Derepression of the flocculati on gene FLO1, which is normally repressed by the Tup1-Ssn6 corepressor, lea ds to its identification as a constitutive Swi-Snf-dependent gene. We demon strate that Tup1-Ssn6 is a chromatin remodelling complex that rearranges an d also orders nucleosomal arrays on the promoter and over 5 kb of upstream intergenic region. Our results confirm that the Swi-Snf complex disrupts nu cleosome positioning on promoters, but reveal that it can also rearrange nu cleosomes several kilobases upstream from the transcription start site. The antagonistic chromatin remodelling activities of Swi-Snf and Tup1-Ssn6 det ected in an array of 32 nucleosomes upstream of FLO1 extend far beyond the scale of promoter-based models of chromatin-mediated gene regulation. The S wi-Snf coactivator and Tup1-Ssn6 corepressor control an extensive chromatin domain in which regulation of the FLO1 gene takes place.