FIGURE 4.

Identification of GRK phosphorylation sites in the D₂ DAR via site-directed mutagenesis. Cells were transfected with the WT D₂ DAR or the indicated Ser/Thr mutant receptors, along with GRK2. Serine and threonine residues were mutated to alanine and valine, respectively. [³²P]H₃PO₄-labeled cells were stimulated with 1 μm DA for 20 min and processed as described in Fig. 1. A representative autoradiogram is shown in the top panel. Autoradiograms from multiple experiments were scanned and quantified as described in Fig. 1. These data are presented as a percentage of the basal phosphorylation of the WT D₂ DAR and expressed as mean ± S.E. values from at least four independent experiments.