Human plasma membrane Ca2+-ATPase (PMCA) isoforms are encoded by at least four separate genes and the diversity of these enzymes is further increased by alternative splicing of transcripts. Cloned cDNAs for two of these isoforms have been used as probes to localize chromosomally the human PMCA1 (ATP2B1) gene to 12q21-q23 and PMCA4 (ATP2B2) to 1q25-q32. These results were obtained by three independent methods, including Southern analysis of human-rodent somatic cell hybrids, in situ hybridization of human metaphase spreads, and genetic linkage analysis in the CEPH pedigrees. High-frequency RFLPs detected at each locus were used in these linkage analyses. No evidence was obtained for multiple copies of the gene at either locus. A cross-hybridizing sequence was detected with PMCA4 probes on Xq13-qter at low stringency. Further studies are required to determine whether this X-chromosomal sequence represents a third member of the PMCA gene family.
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