DNA-binding domain of heptocyte nuclear factor 4 (HNF4) is composed of two C4-type zinc fingers
DNA-binding domain of hepatocyte nuclear factor 4 (HNF4) is composed of two C4-type zinc fingers. Each zinc finger contains a group of four Cys residues which co-ordinates a single zinc atom. HNF4 interacts with a DNA site, composed of two direct repeats of AGTTCA with 1 bp spacer, which is upstream of target genes and modulates the rate of transcriptional initiation. HNF4 is a member of the nuclear receptor superfamily. HNF4 plays a key role in establishing and maintenance of hepatocyte differentiation in the liver. It is also expressed in gut, kidney, and pancreatic beta cells. HNF4 was originally classified as an orphan receptor, but later it is found that HNF4 binds with very high affinity to a variety of fatty acids. However, unlike other nuclear receptors, the ligands do not act as a molecular switch for HNF4. They seem to constantly bind to the receptor, which is constitutively active as a transcription activator. Like other members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors, HNF4 has a central well conserved DNA binding domain (DBD), a variable N-terminal domain, a flexible hinge and a C-terminal ligand binding domain (LBD).