a, Spectrophotometric assay of PKA-Cɑ substrate phosphorylation, in the presence of standard (red) or extended (coral) SMO peptides (see Fig. 1a) or a control PKIα(5–24) peptide (grey). b, Concentration dependent inhibition of PKA-Cɑ with recombinant SMO pCT. c, As a, but comparing wild-type vs. WRR mutant versions of the recombinant SMO pCT.Inhibition in a-c is calculated relative to a control without SMO or PKIα(5–24) peptide (Ctrl.). Data in a-c is shown as the mean +/− standard deviation of two independent experiments. P < 0.001 (***); P < 0.0001 (****), n.s. = not significant. See Supplementary Table 1 for full statistical analysis.