Acts as a transcriptional regulator that recognizes and binds to the sequence 5'-[GA]TTA[CT]GTAA[CT]-3', a sequence present in many cellular and viral promoters. Represses transcription from promoters with activating transcription factor (ATF) sites (By similarity). Represses promoter activity in osteoblasts. Represses transcriptional activity of PER1. Represses transcriptional activity of PER2 via the B-site on the promoter. Activates transcription from the interleukin-3 promoter in T-cells (By similarity). Competes for the same consensus-binding site with PAR DNA-binding factors (DBP, HLF and TEF). Component of the circadian clock that acts as a negative regulator for the circadian expression of PER2 oscillation in the cell-autonomous core clock. Protects pro-B cells from programmed cell death. Represses the transcription of CYP2A5 (PubMed:30555544). Positively regulates the expression and activity of CES2 by antagonizing the repressive action of NR1D1 on CES2 (PubMed:29653076). Required for the development of natural killer cell precursors (PubMed:32190943). Homodimer (By similarity). Binds DNA as a dimer (By similarity). Interacts with DR1 (By similarity). Interacts with PER2 and CRY2 (PubMed:17274955). Interacts with NR0B2 (PubMed:30555544). Interacts with NR1D1 (PubMed:29653076). Interacts with MYSM1 (By similarity). Expressed in suprachiasmatic nucleus and liver (at protein level). Expressed in suprachiasmatic nucleus, hippocampus, gyrus dentatus, piriform cortex, internal granular layer of olfactory bulb, dorsomedial hypothalamic nucleus, pontine nuclei, granular layer of cerebellum, liver and calvariae osteoblasts. Expressed in natural killer cell precursors in bone marrow (PubMed:32190943). Expression is regulated by circadian rhythms. Up-regulated by parathyroid hormone (PTH) (at protein level). Up-regulated by IL-3, forskolin, 8-bromo-cAMP, phorbol myristate acetate and PTH in primary osteoblasts and calvariae. Reduced number of natural killer cell-committed progenitors in bone marrow. Belongs to the bZIP family. NFIL3 subfamily.