The function of SAG (S-antigen visual arrestin, Ensembl gene identifier ENSG00000130561) is as follows. Binds to photoactivated, phosphorylated RHO and terminates RHO signaling via G proteins by competing with G proteins for the same binding site on RHO (By similarity). May play a role in preventing light-dependent degeneration of retinal photoreceptor cells (PubMed:9565049). {ECO:0000250|UniProtKB:P08168, ECO:0000305|PubMed:9565049}.