INTRON SEQUENCE DIRECTS RNA EDITING OF THE GLUTAMATE-RECEPTOR SUBUNITGLUR2 CODING SEQUENCE

The Ca2+ permeability and the rectifying properties of the glutamate r eceptors assembled from the subunits GluR1-GluR4 depend upon a critica l Arg in the GluR2 subunit located in a domain that has been proposed to span the membrane. The GluR2 subunit gene encodes a Gin (CAG) at th is position, whereas the mRNA is edited so that it encodes an Arg (CGG ) at this position [Sommer, B., Kohler, M., Sprengel, R. & Seeburg, P. H. (1991) Cell 67, 11-20]. The editing process is specific since only the GluR2 subunit RNA is edited even though the GluR1, GluR3, and Glu R4 RNAs have a similar sequence. We show that this selective RNA editi ng depends upon a critical intron sequence in the GluR2 gene. This cri tical intron sequence is sufficient to cause editing of the GluR3 subu nit exon in a chimera minigene constructed so that the GluR3 exon is p laced upstream to the GluR2 intron sequence. Transfections of a neuron al cell line, N2a, with minigene constructs encoding different fragmen ts of the GluR2 gene demonstrate that the 5' part of the 3' intron is essential for editing. Part of the exon and this critical intron seque nce contains an inverted repeat that can fold into a structure consist ing of three helical elements. Similar conclusions were reached by Hig uchi, M., Single, F. n., Kohler, M., Sommer, B., Sprengel, R. and Seeb urg, P. H. [(1993) Cell 75, 1361-1370]. These experiments demonstrate that the low Ca2+ permeability of the ionotropic non-N-methyl-D-aspart ate glutamate receptors depends upon RNA editing, which requires a seq uence in an intron 3' to the exon.