Invited Symposium: Molecular Physiology of Sodium-Calcium Exchange
Lytton, J. (Biochemistry & Molecular Biology, University of Calgary, Canada)
Northern blots of Na/Ca exchanger, NCX1, expression have revealed a major transcript of ~7 kb, a minor transcript of ~4 kb and a relatively abundant 1.8 kb transcript. The 1.8 kb transcript is not polyadenylated, and is detected only with a probe spanning the exon-2 region. The tissue and sub-cellular distribution of the 1.8 kb transcript matched that of full-length NCX1. By a combination of inverse-PCR, RT-PCR, and affinity isolation studies, we conclude that the 1.8 kb transcript corresponds to a perfectly circularized exon-2 species. The circular transcript contains the normal NCX1 start codon, a new stop codon introduced as a consequence of circularization, and encodes a protein corresponding to the N-terminal portion NCX1, terminating just after amino acid 600 in the cytoplasmic loop. A linear version of the circular transcript was prepared and transfected into HEK-293 cells. As protein, matching the predicted size of ~70 kDa, was expressed, and the transfected cells possessed Na/Ca transport activity. Although in native tissue we could not detect a protein corresponding exactly to that predicted from the circular transcript, a prominent band of slightly shorter size, possibly representing further proteolytic processing of circular transcript protein, was observed.
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|Li, X.-F.; Lytton, J.; (1998). A Circularized Sodium-Calcium Exchanger Exon-2 Transcript. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Invited Symposium. Available at URL http://www.mcmaster.ca/inabis98/lytton/li0411/index.html|
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