The regulator of G protein signaling 19 protein (RGS19/GAIP) which has been shown to modulate signaling of the mu opioid receptor, is located immediately upstream of OPRL1, and is transcribed from the opposite strand. The two genes (RGS19, OPRL1) share their promoter (Ito et al. 2000; Xie et al. 2007). Two unique repeat polymorphisms were described in the promoter region but no significant effect on promoter activities was found (Ito et al. 2000).
