Potassium channel mRNAs with AU-rich elements and brain-specific expression.

GIRK2 (G protein-gated inwardly rectifying K(+) channel 2) located on the Down syndrome region 21q22.2 in humans has been reported to have several alternative transcripts and transcripts longer than 4 kb that do not have the poly-A tail. We sequenced GIRK2 transcripts with a long 3'-untranslated region (3'-UTR) containing multiple adenylate uridylate-rich elements (AREs) with the poly-A tail. In a 16-kb transcript, 28 AUUUA pentanucleotides, 9 AUUUUA hexanucleotides, 5 AUUUUUA heptanucleotides, and 3 UUAUUUA[U/A][U/A] nonanucleotides were found. Northern blot and in situ hybridization revealed abundant expression of the 16-kb transcripts in the rat brain despite no detectable signals in other tissues examined. The AREs have been reported to mediate the turnover of mRNAs encoding proteins regulating cellular proliferation/differentiation and body response to inflammatory and environmental stimuli. This is the first study indicating that ion channel transcripts have multiple AREs.