CAPN5 and CAPN6 are recently identified human and mouse genes lacking a calmodulin-like domain with homology to the calpain family of proteases. To clarify their relationship to the known calpains, we have compared their genomic organization and chromosome location with other human calpain gene family members. In the mouse, both genes have 11 introns of identical location, with 6 of these being similar in location to those of the known vertebrate members. Surprisingly, there were no splice junctions in common with the nematode gene tra-3, the calpain with highest homology to CAPN5 and CAPN6. CAPN5 is localized on human chromosome 11, closely linked to the μ- calpain gene CAPN1. CAPN6, which is expressed only in the placenta, is localized on the X chromosome, to which no other calpain has yet been mapped.
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