NFIL3,also named as E4BP4 and IL3BP1,belongs to the bZIP family and NFIL3 subfamily. It represses transcription from promoters with activating transcription factor (ATF) sites. NFIL3 activates transcription from the interleukin-3 promoter in T-cells. It competes for the same consensus-binding site with PAR DNA-binding factors (DBP,HLF and TEF). It is a component of the circadian clock that acts as a negative regulator for the circadian expression of PER2 oscillation in the cell-autonomous core clock. NFIL3 protects pro-B cells from programmed cell death. It is a key regulator of TH2 responses.