Catalytic component of the RPD3 histone deacetylase (HDAC) complexes RPD3C(L) and RPD3C(S) responsible for the deacetylation of lysine residues on the N-terminal part of the core histones (H2A, H2B, H3 and H4). Histone deacetylation plays an important role in transcriptional regulation, cell cycle progression, DNA damage response, osmotic stress response and developmental events. Is involved in rDNA and telomere silencing and in double strand breaks repair. Required for both full transcription repression and activation of many genes including cell type-specific genes (STE6, TY2 and HO), cell differentiation-specific genes (SPO13), genes that respond to external signals (PHO5) and TRK2. The RPD3 complexes regulate also chromosomal replication timing. H2O + N(6)-acetyl-L-lysyl-[histone] = acetate + L-lysyl-[histone] Component of the RPD3C(L) complex composed of at least ASH1, CTI6, DEP1, PHO23, RPD3, RXT2, RXT3, SAP30, SDS3, SIN3, UME1 and UME6. Component of the RPD3C(S) complex composed of at least EAF3, RCO1, RPD3, SIN3, and UME1. Interacts with cyclophilins CPR1, CPR6 and CPR7, with the kinase HOG1, and with ESS1, CYC8 and HAC1. The ESA1-RPD3 (ER) motif is common to ESA1 and RPD3 and is required for ESA1 histone acetyl-transferase (HAT) activity and RPD3 histone deacetylase (HDAC) activity. Heterochromatin spreading downstream of the silent mating-type locus HMR. Present with 3850 molecules/cell in log phase SD medium. Belongs to the histone deacetylase family. HD type 1 subfamily.