Nuclear receptors gene structure. The six regions (A-F) of nuclear receptors. The A/B region contains the AF-1 activation function. The highly conserved central DNA-binding-domain DBD (C region) comprises two zinc fingers, including the P-box and D-box. The ligand-binding-domain LBD (E region) contains the AF-2 activation function helix. Situated between the DBD and the LBD is the variable “hinge” region (D region). The C-terminal region F is located at the end of the NR and varies in length among different nuclear receptors.