Identification of a putative isoform of the Na,K-ATPase β subunit. Primary structure and tissue-specific expression

We have isolated cDNA clones from rat brain and human liver encoding a putative isoform of the Na,K-ATPase β subunit. The rat brain cDNA contains an open reading frame of 870 nucleotides coding for a protein of 290 amino acids with a calculated molecular weight of 33,412. The corresponding amino acid sequence shows 98% identity with its human liver counterpart. The proteins encoded by the rat and human cDNAs exhibit a high degree of primary sequence and secondary structure similarity with the rat Na,K-ATPase β subunit. We have therefore termed the polypeptides these cDNAs encode a β2 subunit with the previously characterized rat cDNA encoding a β1 subunit. Analysis of rat tissue RNA reveals that the β2 subunit gene encodes a 3.4-kilobase mRNA which is expressed in a tissue specific fashion distinct from that of rat β1 subunit mRNA. Cell lines derived from the rat central nervous system shown to lack β1 subunit mRNA sequences were found to express β2 subunit mRNA. These results suggest that different members of the Na,K-ATPase β subunit family may have specialized functions.