IDENTIFICATION OF THE MAMMALIAN NA,K-ATPASE BETA-3 SUBUNIT

We have isolated and characterized cDNA clones encoding the human and rat Na,K-ATPase beta 3 subunit isoform, The human cDNA encodes a polyp eptide of 279 amino acids that exhibits primary sequence and secondary structure similarities to Na,K-ATPase beta subunit isoforms. Sequence comparisons showed that the human beta 3 subunit closely resembles th e beta 3 subunit of Xenopus laevis (59% amino acid identity) and is le ss similar to the human Na,K-ATPase beta 1 and beta 2 subunits (38% an d 48% amino acid identity, respectively). By analyzing the segregation of restriction fragment length polymorphisms among recombinant inbred strains of mice, we localized the beta 3 subunit gene to murine chrom osome 7. Northern blot analysis revealed that the beta 3 subunit gene encodes two transcripts that are expressed in a variety of rat tissues including testis, brain, kidney, lung, stomach, small intestine, colo n, spleen, and liver. Identification of the mammalian beta 3 subunit s uggests an even greater potential for Na,K-ATPase isoenzyme diversity than previously realized.