NCOR1 (Nuclear Receptor Corepressor 1) is a protein that plays a key role in regulating gene expression and transcriptional repression. Located mainly in the cell nucleus, NCOR1 modulates the activity of nuclear receptors and other transcription factors. It functions as a corepressor for receptors such as thyroid hormone receptors (TRs), retinoic acid receptors (RARs), and peroxisome proliferator-activated receptors (PPARs). By recruiting histone deacetylases (HDACs) and other chromatin-modifying enzymes, NCOR1 helps form repressive chromatin structures, leading to reduced gene transcription.