Structure of the human CALM1 calmodulin gene and identification of two CALM1-related pseudogenes CALM1P1 and CALM1P2.

The human CALM1 calmodulin gene has been isolated and characterized. The gene contains six exons spread over about 10 kb of genomic DNA. The exon-intron structure is identical to that of the human CALM3 and of the rat CALM1 and CALM3 genes. A cluster of transcription-start sites was identified 200 bp upstream of the ATG translation-start codon, and several putative regulatory elements were found in the 5' flanking region as well as in intron 1. Sequence comparison with the rat CALM1 gene revealed significant similarities in the promoter regions of the two genes and an even more striking degree of identity (70%) in the available intron 1 sequences. A short CAG trinucleotide repeat region was identified in the 5' untranslated region of the human CALM1 gene; this sequence is not conserved in the rat counterpart. Expression of the CALM1 gene was detected in all human tissues tested, although at varying levels. A 1.7-kb mRNA was uniformly present at comparable levels, whereas a 4.2-kb mRNA species was particularly abundant in brain and skeletal muscle. Clones for two different CALM1-related pseudogenes CALM1P1 and CALM1P2 were also isolated and characterized. Both pseudogenes are intronless and non-functional as judged from the presence of mutations abolishing the open reading frame. Genomic Southern analysis indicates that the human CALM1 gene/pseudogene subfamily comprises at least three but probably no more than four members. The entire family consists of three bona fide CALM genes, at least one expressed calmodulin-like CALML gene as well as at least five pseudogenes.