Transcriptional repressor which coordinates circadian rhythm and metabolic pathways in a heme-dependent manner. Integral component of the complex transcription machinery that governs circadian rhythmicity and forms a critical negative limb of the circadian clock by directly repressing the expression of core clock components ARNTL/BMAL1 and CLOCK. Also regulates genes involved in metabolic functions, including lipid metabolism and the inflammatory response. Acts as a receptor for heme which stimulates its interaction with the NCOR1/HDAC3 corepressor complex, enhancing transcriptional repression. Recognizes two classes of DNA response elements within the promoter of its target genes and can bind to DNA as either monomers or homodimers, depending on the nature of the response element. Binds as a monomer to a response element composed of the consensus half-site motif 5'-[A/G]GGTCA-3' preceded by an A/T-rich 5' sequence (RevRE), or as a homodimer to a direct repeat of the core motif spaced by two nuclegotides (RevDR-2). Acts as a potent competitive repressor of ROR alpha (RORA) function and also negatively regulates the expression of NR1D1. Regulates lipid and energy homeostasis in the skeletal muscle via repression of genes involved in lipid metabolism and myogenesis including: CD36, FABP3, FABP4, UCP3, SCD1 and MSTN. Regulates hepatic lipid metabolism via the repression of APOC3. Represses gene expression at a distance in macrophages by inhibiting the transcription of enhancer-derived RNAs (eRNAs). In addition to its activity as a repressor, can also act as a transcriptional activator. Acts as a transcriptional activator of the sterol regulatory element-binding protein 1 (SREBF1) and the inflammatory mediator interleukin-6 (IL6) in the skeletal muscle. Plays a role in the regulation of circadian sleep/wake cycle; essential for maintaining wakefulness during the dark phase or active period (PubMed:29355503). Key regulator of skeletal muscle mitochondrial function; negatively regulates the skeletal muscle expression of core clock genes and genes involved in mitochondrial biogenesis, fatty acid beta-oxidation and lipid metabolism (PubMed:29723273). May play a role in the circadian control of neutrophilic inflammation in the lung (PubMed:29533925). The heme-bound form can bind gaseous signaling molecules such as CO and nitric oxide (NO) and NO can reverse its transcriptional repressor activity. Binds DNA as a monomer or a homodimer (By similarity). Interacts with NCOA5 coactivator, leading to a strong increase of transcription of target genes (By similarity). Interacts (via N-terminus) with KAT5 (By similarity). Interacts (via C-terminus) with HDAC1 (By similarity). Interacts with ZNHIT1 (By similarity). Interacts with SIAH2 (By similarity). Phosphorylation by CSNK1E enhances its cytoplasmic localization. Ubiquitous. Expressed abundantly in skeletal muscle and brown adipose tissue. Expressed during skeletal muscle myogenesis. Activated by the CLOCK-ARNTL/BMLA1 heterodimer and DBP and repressed by CRY1. Composed of three domains: a modulating N-terminal domain, a DNA-binding domain and a C-terminal ligand-binding domain. Deacetylated by HDAC1 (By similarity). Acetylation and deacetylation regulate its transcriptional regulatory activity (By similarity). Under more reducing intracellular redox conditions, Cys-381 is in its heme-bound state, which is optimal for recruitment of the NCOR1/HDAC3 corepressor complex and repression of target genes (By similarity). When subjected to oxidative stress conditions, Cys-381 undergoes oxidation to form a disulfide bridge with Cys-371, also triggering a ligand switch that results in release of bound heme and derepression of target genes (By similarity). Ubiquitinated by SIAH2; leading to its proteasomal degradation. Phosphorylated by CSNK1E; phosphorylation enhances its cytoplasmic localization. Mice exhibit an altered circadian metabolism and feeding schedule, eating more and utilizing more carbohydrates as fuel during their nocturnal/sleep period (PubMed:29723273). Increased expression of circadian clock core genes and genes involved in lipid metabolism and fatty-acid oxidation in the skeletal muscle (PubMed:29723273). Mice exhibit decreased wakefulness and increased slow-wave sleep and rapid eye movement sleep during the dark phase (active period) (PubMed:29355503). Altered expression in the brain of core circadian clock genes and genes involved in sleep induction and wakefulness (PubMed:29355503). Conditional knockout of both NR1D1 and NR1D2 in bronchiolar epithelial cells abolished diurnal rhythmicity of PER2 in the bronchioles and increased inflammatory responses and chemokine activation (PubMed:29533925). Belongs to the nuclear hormone receptor family. NR1 subfamily.