Regulatory protein which represses transcription and augments histone deacetylase activity of HDAC1. May have a potential role in tumor suppressor pathways through regulation of apoptosis. May function in the assembly and/or enzymatic activity of the mSin3A corepressor complex or in mediating interactions between the complex and other regulatory complexes. {ECO:0000269|PubMed:12724404, ECO:0000269|PubMed:21239494}. This is the function of SUDS3 (SIN3A corepressor complex component SDS3, ENSG00000111707).