Frizzled receptors have long been thought to couple to G proteins but biochemical evidence supporting such an interaction has been lacking. Here we expressed mammalian Wnt-Frizzled fusion proteins in Saccharomyces cerevisiae and tested the receptors’ ability to activate the yeast mitogen-activated protein kinase (MAPK) pathway via heterotrimeric G proteins. Our results show that Frizzled receptors can interact with Gαi, Gαq, and Gαs proteins, thus confirming that Frizzled functions as a G protein coupled receptor (GPCR). However, the activity level of Frizzled-mediated G protein signaling was much lower than that of a typical GPCR and, surprisingly, was highest when coupled to Gαs. The Frizzled/Gαs interaction was further established in vivo as Drosophila expressing a loss-of-function Gαs allele rescued the photoreceptor differentiation phenotype of Frizzled mutant flies. Together, these data point to an important role for Frizzled as a nontraditional GPCR that preferentially couples to Gαs heterotrimeric G proteins.

The surface-induced and electron-induced chemistry of trifluoroiodomethane (CF3I), a potential replacement for chlorofluorocarbons (CFCs) and chlorofluorobromocarbons (halons), were investigated under ultrahigh vacuum conditions (p ∼ 1 × 10-10 Torr) on Mo(110). Results of temperature-programmed desorption (TPD) experiments indicate that dissociative adsorption of CF3I leads only to nonselective decomposition on Mo(110), in contrast to reactions of CF3I on other metal surfaces. Desorption of CF3 radicals and atomic iodine was detected mass spectrometrically during low-energy (10−100 eV) electron irradiation of four monolayer thick films of CF3I condensed at 100 K. Results of postirradiation temperature-programmed desorption experiments were used to identify CF2I2, C2F5I, C2F6, C2F4I2, and CFI3 as electron-induced reaction products of CF3I. Except for CFI3, all of these electron-induced reaction products of CF3I have been previously identified in γ-radiolysis studies, supporting our earlier claim that temperature-programmed desorption experiments conducted following low-energy electron irradiation of multilayer thin films provide an effective method to investigate the effects of high-energy radiation, including radical−radical reactions.

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