In vitro binding of RGS3 to Gα proteins. An RGS3-GST fusion protein was incubated with 35S-Met-Gα proteins, and glutathione beads were used to "pull-down" the RGS3-GST/Gα protein complex. The amount of 35S-Gα protein bound was determined by SDS/PAGE separation, and quantification using a Phosphor imaging device. The data point for each G protein is the fraction of its total cpm that were bound to RGS3-GST fusion protein after subtraction of the cpm bound to control GST fusion protein. Mean ± SEM of three independent experiments. Gqα, Gzα, and Gi3α were not significantly different from the other Gα-proteins (p < 0.05) that, in turn, were significantly higher than a group to which 35S-Met alone was added (p < 0.05).