RGS9 (regulator of G protein signaling 9) is a critical regulator of phototransduction in retinal photoreceptors that functions as a GTPase activating protein (GAP) to terminate G protein signaling cascades 1. The gene produces two alternatively spliced isoforms: RGS9-1, which is specifically expressed in rod and cone photoreceptors, and RGS9-2, expressed in brain regions including the basal ganglia 12. RGS9-1 accelerates GTP hydrolysis of activated G protein alpha subunits, particularly GNAT1 in phototransduction, driving them to their inactive GDP-bound state and enabling rapid recovery of photoresponses 34. This function is essential for normal subsecond recovery kinetics of light responses in photoreceptors 3. The protein's activity is regulated by calcium-dependent phosphorylation at serine 475, with phosphorylation levels reduced by light exposure 5. RGS9-1 requires interaction with Gβ5 proteins for stability and proper function 3. Pathogenic variants in RGS9 are associated with inherited retinal diseases, including prolonged electroretinal response suppression, highlighting its clinical significance in visual function 6. The protein represents a key therapeutic target for understanding phototransduction disorders and developing treatments for inherited retinal diseases.