Activity and Expression Levels of α
-GFP Fusion Proteins. (A) HEK 293 cells were transfected with 2 μg/106 cells of the indicated αs-GFP constructs or vector alone (pcDNA1/Amp) and 0.2 μg/106 cells of plasmid encoding the LH receptor. cAMP accumulation was measured in the presence (dark gray bars) or absence (light gray bars) of hCG, an LH receptor agonist. Cells expressing each of the αs-GFP fusion proteins exhibited increased basal and stimulated cAMP accumulation relative to cells expressing vector alone, but only the increases in cells expressing αs-GFP(92–94) were significantly greater (p < .05). Values represent the mean ± S.E. of 5 independent experiments. (B) Immunoblots of the membrane pellets (P) and supernatant (S) fractions from transiently transfected HEK 293 cells. Expression levels of tribrid fusion proteins αs-GFP(18–20) and αs-GFP(92–94), but not of amino- and carboxy-terminus fusions, αs-GFP(N) and αs-GFP(C), respectively, were decreased in both fractions relative to that of unlabeled αsEE. Similar results were obtained in an additional experiment.