Cloning of the H,K-ATPase β subunit: Tissue-specific expression, chromosomal assignment, and relationship to Na,K-ATPase β subunits

We have isolated cDNA clones encoding the bovine and rat gastric H,K-ATPase β subunit. A bovine abomasum λgt11 cDNA library was screened with a monoclonal antibody raised against the rabbit H,K-ATPase β subunit. A single positive phage clone containing an ∼900-base pair cDNA insert was identified as reactive with the antibody. The identity of the cDNA was established by comparing the deduced amino acid sequence with sequences of cyanogen bromide fragments of the porcine H,K-ATPase β subunit. Polymerase chain reaction and rapid amplification of cDNA ends were used to generate a cDNA fragment encoding the carboxyl-terminal portion of the rat gastric H,K-ATPase β subunit. A rat stomach cDNA library was screened with the polymerase chain reaction product, and several full-length β subunit cDNA clones were identified. The open reading frame predicts a protein of 294 amino acids with a molecular weight of 33,689. The rat H,K-ATPase β subunit shows 41% amino acid sequence identity to the rat Na,K-ATPase β2 subunit and shares a number of structural similarities with Na,K-ATPase β subunit isoforms. By analyzing the segregation of restriction fragment length polymorphisms among recombinant inbred strains of mice, we localized the H,K-ATPase β subunit gene to murine chromosome 8. Northern and Western blot analysis reveals that this gene is expressed exclusively in stomach. Our results suggest that the H,K-ATPase and Na,K-ATPase β subunits evolved from a common ancestral gene and may play similar functional roles in enzyme activity.