We have characterized the nucleotide sequence of Na+/K+-ATPase alpha subunit (NKA) cDNA in embryos of the sea urchin, Hemicentrotus pulcherrimus. The primer extension experiments showed that the sea urchin NKA gene generated multiple lengths of transcript. To obtain the 5′-ends of the transcripts, we isolated cDNA clones by the rapid amplification of cDNA ends (RACE). These clones were classified into 2 types on the basis of their 5′ leader sequences. The sequences of the clones were identical except their 5′ leaders. By Northern blot analysis, 1 of the 2 types of transcripts was always detectable in sea urchin embryos during early development, and another was not detected before the morula stage. Genomic PCR demonstrated that the two 5′ leaders were coded by different exons separated by an intron in a single gene. These results show that the transcripts coding 2 isoforms were expressed from a single gene.
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