Transcriptional regulator; functions primarily as a transcriptional co-repressor with Tup1p but can also function as a transcriptional co-activator with Tup1p that recruits the SWI/SNF and SAGA complexes to promoters; target genes may be uniquely repressed by Cyc8p or Tup1p, subject to redundant repression, or in some cases de-repression of target genes in a cyc8 mutant is dependent upon TUP1 and vice versa; can form the prion [OCT+]