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Abstract

L-glutamate, the principal excitatory transmitter in the brain, gates ion channels mediating fast neurotransmission. Subunit components of two related classes of glutamate receptor channels have been characterized by cDNA cloning and shown to carry either an arginine or a glutamine residue in a defined position of their putative channel-forming segment. The arginine residue in this segment profoundly alters, and dominates, the properties of ion flow, as demonstrated for one channel class. We now show that the genomic DNA sequences encoding the particular channel segment of all subunits harbor a glutamine codon (CAG), even though an arginine codon (CGG) is found in mRNAs of three subunits. Multiple genes and alternative exons were excluded as sources for the arginine codon; hence, we propose that transcripts for three subunits are altered by RNA editing. This process apparently edits subunit transcripts of the two glutamate receptor classes with different efficiency and selectivity.