Transcriptional regulator; functions primarily as a transcriptional co-repressor with Cyc8p but can also function as a co-activator, recruiting SWI/SNF and SAGA complexes to promoters; target genes may be uniquely repressed by Tup1p or Cyc8p, subject to redundant repression, or in some cases de-repression of target genes in a tup1 mutant is dependent upon CYC8 and vice versa; establishes a repressive chromatin structure via histone H3/H4 interactions and stabilizing nucleosomes over promoters