Fig. 3. Alignment of the fly Smo protein with the zebrafish/mouse Smo. The transmembrane (TM) domain and the N-terminal regions of the protein are relatively conserved from fly to mammals. The cysteine-rich domains (CRDs) in fish and mouse smoothened (Smo) are very similar (70% identical, 82% similar), while the CRD in fly Smo is more divergent (43% identical, 56% similar between fly and mouse). C-terminal to the 180 residues adjacent to the 7th TM domain of Drosophila Smo, there are only short patches of homology between Drosophila Smo and either the zebrafish or the mouse Smo, whereas this region is relatively conserved (31% identity) between zebrafish and mouse Smo. This same region in flies is important for binding to Cos2, indicating that the interaction between Smo and Cos2 is not conserved in vertebrates. The protein kinase A phosphorylation sites in the fly Smo protein are not conserved. PKA, protein kinase A.