Structural organization and transcription of the mouse gastric H⁺,K⁺-ATPase β subunit gene

We have cloned and characterized the mouse gene encoding the β subunit of H⁺,K⁺-ATPase (EC 3.6.1.36). The entire 10.5-kilobase transcription unit of the H⁺,K⁺-ATPase β subunit gene was cloned in three overlapping cosmids encompassing ≈46 kilobases of genomic DNA. A tight cluster of transcription initiation sites has been localized 24-25 nucleotides upstream of the translation start site and 28-29 nucleotides downstream of a TATA-like sequence. The H⁺,K⁺-ATPase β subunit gene is split into seven exons encoding predicted structural domains of the β subunit protein. The intracellular amino-terminal and putative transmembrane domains are encoded by individual exons, and the extracellular carboxyl-terminal domain is encoded by five exons. The exon/intron organization of the mouse H⁺,K⁺-ATPase β subunit gene is identical to that of the mouse Na⁺,K⁺-ATPase β2 subunit gene. The conservation of genomic organization, together with the high sequence homotogy, indicates that the noose H⁺,K⁺-ATPase β and Na⁺,K⁺-ATPase β2 subunit genes originated from a common ancestral gene.