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Abstract:
Sequence variation was found in cDNA coding for the extracellular domain of the rat gamma−aminobutyric acid type A (GABAA) receptor alpha 6 subunit. About 20% of polymerase chain reaction (PCR)−amplified alpha 6 cDNA prepared from rat cerebellar mRNA lacked nucleotides 226−255 as estimated by counting single−stranded phage plaques hybridized specifically to the short (alpha 6S) and long (wild−type) forms of the alpha 6 mRNA. Genomic PCR revealed an intron located upstream of the 30−nucleotide sequence. Both splice forms were detected in the cerebellum by in situ hybridization. Recombinant receptors, resulting from coexpression of the alpha 6S subunit with the GABAA receptor beta 2 and gamma 2 subunits in human embryonic kidney 293 cells, were inactive at binding [3H]muscimol and [3H]Ro 15−4513. In agreement, injection of complementary RNAs encoding the same subunits into Xenopus oocytes produced only weak GABA−induced currents, indistinguishable from those produced by beta 2 gamma 2 receptors. Therefore, the 10 amino acids encoded by the 30−nucleotide fragment may be essential for the correct assembly or folding of the alpha 6 subunit−containing receptors
