The hepatitis B virus X-associated protein (XAP2, also designated AIP and ARA9) and the heat shock protein p23. XAP2, a ubiquitously expressed protein, binds to HSP 90 and AhR through a highly conserved carboxy-terminal tetraticopeptide repeat domain. XAP2 participates in stabilizing AhR as well as enhancing the cytoplasmic localization of the receptor. It may also be involved in regulating the degradation of AhR.
