The binding of indicated mutants of bovine arrestin-2 and −3 to P-Rh* was determined, as described in Methods. Abbreviations: KA – K294A or K295A in arrestin-2 and −3, respectively; RE – R169E or R170E in arrestin-2 and −3, respectively. Means +/− SD are shown. Dots represent individual measurements (n=6). Statistical significance of the differences between KA mutants and corresponding arrestins carrying WT lysine in the lariat loop was determined by ANOVA with post-hoc correction for multiple comparisons and is indicated, as follows: **, p<0.01; ***p < 0.001; ns, not significant.