P-type ATPases are a venerable family of ATP-dependent ion transporters. Recently, evidence was presented that a rabbit gene in the type IV subfamily of P-type ATPases was missing a transmembrane helix (TM4) thought to be critical for ion transport, a deletion which would place the two major catalytic loops of the enzyme on opposite sides of the membrane. It was proposed that the resulting protein was a RING finger-binding protein which targets transcription factors to specific domains within the nucleus. From analysis of human genomic sequence data, it is shown here that the region containing TM4, corresponding to exon 12, is present in the human homolog of the gene, ATP11B. PCR analysis indicates that the predominant Atp11b transcripts in a rabbit and in a mouse cDNA library also contain exon 12. The results suggest that the transcript proposed to encode the RING finger-binding protein is a minor rabbit-specific splice variant. The ATP11B gene thus may not encode a protein with a function radically different from other P-type ATPase transporters.