Predicted domain structure and transmembrane topology for RhoPDE. Domain nomenclature: N-term, N-terminal domain; Rho, microbial type I rhodopsin domain; linker, sequence connecting the Rho and PDE domains; PDE, phosphodiesterase domain; and C-term, short C-terminal domain. Transmembrane helices were predicted and drawn with Protter (wlab.ethz.ch/protter/start).8 Amino acids are colored: green, Lys296 (numbering of the native protein), the presumed covalent attachment site for the retinal chromophore; blue, the C8 epitope tag; and orange, the 1D4 epitope tag.