SAP25 is a family of proteins found in eukaryotes. SAP25 is a core component of the mSin3 co-repressor complex whose subcellular location is regulated by PML. mSin3, the transcriptional co-repressor, is associated with histone deacetylases (HDACs) and is utilized by many DNA-binding transcriptional repressors. SAP25 is a nucleo-cytoplasmic shuttling protein that is actively exported from the nucleus by a CRM1-dependent mechanism. It binds to the PAH1 domain of mSin3A, associates with the mSin3A-HDAC complex in vivo, and represses transcription when tethered to DNA.