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-subunit mRNA leads to distinct
NH2-terminal variant
proteins
1 Department of Internal
Medicine,
The amiloride-sensitive epithelial sodium channel (ENaC) is
composed of three subunits:
,
, and
. The human
-ENaC
subunit is expressed as at least two transcripts (N. Voilley, E. Lingueglia, G. Champigny, M. G. Mattei, R. Waldmann, M. Lazdunski, and
P. Barbry. Proc. Natl. Acad. Sci. USA
91: 247-251, 1994). To determine the origin of these transcripts,
we characterized the 5' end of the
-ENaC gene. Four
transcripts that differ at their first exon were identified. Exon 1A
splices to exon 2 to form the 5' end of
-ENaC1, whereas exon
1B arises separately and continues into exon 2 to form
-ENaC2. Other
variant mRNAs,
-ENaC3 and
-ENaC4, are formed by activating
5' splice sites within exon 1B. Although
-ENaC3 and -4 did not
change the open reading frame for
-ENaC,
-ENaC2 contains upstream
ATGs that add 59 amino acids to the previous (
-ENaC1) protein. To
address the significance of these isoforms, both proteins were
expressed in Xenopus oocytes. The cRNA
for each
-ENaC transcript when combined with
- and
-ENaC cRNA
reconstituted a low-conductance ion channel with amiloride-sensitive currents of similar characteristics. We have thus identified variant
-ENaC mRNAs that lead to functional ENaC peptides.
sodium transport; Xenopus oocyte; patch clamp; gene expression; alternate transcripts
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