Acts as component of the CYC8-TUP1 corepressor complex which is involved in the repression of many genes in a wide variety of physiological processes including heme-regulated and catabolite repressed genes. May also be involved in the derepression of at least some target genes. The complex is recruited to target genes by interaction with DNA-bound transcriptional repressors, like MATALPHA2, MIG1, RFX1 and SKO1. The complex recruits histone deacetylases to produce a repressive chromatin structure, interacts with hypoacetylated N-terminal tails of histones H3 and H4 that have been programmed for repression by the action of histone deacetylases and interferes directly with the transcriptional machinery by associating with the RNA polymerase II mediator complex. Associates with TUP1 to form the CYC8-TUP1 (or TUP1-SSN6) corepressor complex that is composed of 4 copies of TUP1 and one copy of CYC8. Interacts with MATALPHA2, CTI6, MIG1, TUP1, SUT1, RFX1, PGD1, HOS1, HOS2 AND RPD3. The prion domain (PrD) is a Gln/Asn (Q/N)-rich domain, which is unstructured in its native, soluble form, and which forms a parallel in-register beta-sheet in its amyloid form. [OCT+] is the prion form of CYC8. [OCT+] is the result of a conformational change of the cellular CYC8 protein that becomes self-propagating and infectious. [OCT+]-aggregates sequester soluble CYC8, resulting in increased levels of iso-2-cytochrome c, defects in sporulation and mating, higher levels of invertase derepression and increased flocculation, reminiscent of a partial loss of function of the CYC8-TUP1 corepressor complex. [OCT+] can be cured by GdnHCl and by inactivation of the molecular chaperone HSP104, which is required for [OCT+] propagation. It is speculated that prion properties of transcription factors may generate an optimized phenotypic heterogeneity that buffers yeast populations against diverse environmental insults. Present with 3890 molecules/cell in log phase SD medium. Belongs to the CYC8/SSN6 family.