ADAR-mediated editing of the GluA2 subunit of the mammalian AMPA receptor. (a) The unedited GluA2 subunit contains a glutamine residue (Q) at the Q/R site (left). ADAR2 can mediate editing of the Q/R site, resulting in a GluA2 subunit that has a positively charged arginine residue (right). (b) When the tetrameric AMPA receptor contains only the unedited form of the GluA2 subunit (light green), the receptor facilitates the flow of calcium ions (left). Incorporation of an edited GluA2 subunit (light green) sharply reduces the calcium permeability of the receptor because of the presence of the large, positive arginine residue (right).