NCOR1 (Nuclear Receptor Corepressor 1) is a protein that plays a vital role in regulating gene expression and transcriptional repression. Primarily located in the cell nucleus, NCOR1 modulates the activity of nuclear receptors and other transcription factors. It acts 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 assists in forming repressive chromatin structures, resulting in decreased gene transcription.