Mutational analysis of GluA1 phosphorylation sites reveals that Ser-831 uniquely controls the generation of GluA1 homomers. HEK 293 cells were transfected with WT GluA1 or phosphodeficient alanine or phosphomimetic aspartate mutants/GluA2 with or without AKAP79-GFP. Shown is a summary graph of the rectification index obtained from currents evoked by a ramp protocol. Data corresponding to individual cells for each condition are indicated by the open circles. Note that manipulation of Ser-831 was the only site in which the phosphodeficient S831A blocked the effect of AKAP79, whereas the corresponding phosphomimetic S831D mimicked the effect of AKAP79. Black asterisk, p < 0.05, compared with GluA1/GluA2. Red asterisk, p < 0.05 compared with GluA1/GluA2 + AKAP79. #, p < 0.05, compared with S831D/GluA2. Error bars, S.E.