Molecular cloning and chromosomal localization of the genes encoding P23k neuron-specific calcium-binding protein family.

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P23k family is a novel EF-hand calcium-binding protein subfamily, considered to be a calcium sensor in neuron of the central nervous system. We initiated a search for the brain member of P23k family in human and mouse. We report here on two novel human cDNAs and mouse hippocalcin gene.Two novel human cDNAs, HLP3 and HLP4, were obtained from a human brain cDNA library. Both cDNA encode a homologous protein with a molecular weight of 23kDa, containing four potential EF-hand motifs. Northern blot analysis revealed that both mRNAs were expressed only in the brain. The HLP3 mRNA was distributed to most of the brain regions, high amounts of the HLP3mRNA were detected in the cerebral cortex and cerebellum. The HLP4mRNA was also found in many regions of the brain, relatively high amounts of the HLP4mRNA were detected in the cerebral cortex and cerebellum. By discordancy analysis using DNAs from human-rodent somatic cell hybrids, the HLP3 and HLP4 genes were mapped to chromosome 2 and 17, respectively.The mouse hippocalcin gene was obtained from a mouse leukocyte genomic library. The mouse hippocalcin gene contains three exons and two introns, which spans approximately 8 kb. Deduced amino acid sequence of mouse hippocalcin is 100% identical to those of the rat and human and structures of hippocalcin genes are highly conserved across species. The transcription termination site was assigned at 860bp from TAG.The multiple transcription initiation sites were assigned at the positions around-180bp. Neither a canonical 'TATA' box, and 'CAAT' box was found in the 5'-flanking region. By Southern blot analysis, the positive bands exactlycoincided with those expected from the cloned gene. Fluorescence in situ hybridization revealed the mouse hippocalcin gene mapped to chromosome 4, region D2-D3.