Component of the RPD3C(L) histone deacetylase complex (HDAC). Responsible for the deacetylation of lysine residues on the N-terminal part of the core histones (H2A, H2B, H3 and H4). Histone deacetylation gives a tag for epigenetic repression and plays an important role in transcriptional regulation, cell cycle progression and developmental events. CTI6 links the SAGA coactivator to the CYC8-TUP1 corepressor. Involved in transcription regulation of heme-regulated genes and required for GCN5 recruitment, histone H3 acetylation and SPT15/TBP binding to promoters. Component of the RPD3C(L) complex composed of at least ASH1, CTI6, DEP1, PHO23, RPD3, RXT2, RXT3, SAP30, SDS3, SIN3, UME1 and UME6. Interacts with CYC8. Under low iron conditions. Present with 1590 molecules/cell in log phase SD medium.