Characterization of isoforms and genomic organization of mouse calumenin

Calumenin is a multiple EF-hand protein located in endo/sarcoplasmic reticulum of mammalian heart and other tissues [J. Biol. Chem. 272 (1997) 18232; Genomics 49 (1998) 331; Biochim. Biophys. Acta 1386 (1998) 121]. In the present study, a new isoform of mouse calumenin (mouse calumenin 2) was cloned by RT-PCR and genomic DNA PCR. The deduced amino acid sequence of mouse calumenin 2 is 315 aa long with the calculated MW of 37,064 and pI of 4.26. It has 92% aa sequence identity to previously identified mouse calumenin [J. Biol. Chem. 272 (1997) 18232] (mouse calumenin 1). The difference in the aa sequence was restricted to the first two EF-hand regions (residues 74-138). Northern blot analysis shows that mouse calumenin 2 is highly expressed in heart, lung, testis and unpregnant uterus. The expression of mouse calumenin 2 appears to decrease when fetal development is progressed. Genomic DNA PCR, sequencing and data mining of mouse genome database were utilized to examine the exon-intron boundaries of mouse calumenin genes. Both mouse calumenin 1 and 2 genes encompass six exons, and five of them (Exon 1, 3, 4, 5 and 6) are identical. However, mouse calumenin 1 contains Exon2-1, whereas mouse calumenin 2 contains a neighboring Exon2-2. The calumenin genes are localized on mouse chromosome 6 having conserved synteny with human chromosome 7q32. For comparison, the genomic organization of human calumenin was also examined using the published human genome database (UCSC Genome Bioinformatics at http://genome.ucsc.edu/). Like mouse calumenin genes, two human calumenin genes also consist of five identical exons (Exon 1, 3, 4, 5 and 6) and a different Exon2. The present study suggests that the genomic organization of calumenin genes is well conserved between human and mouse. (C) 2003 Elsevier B.V. All rights reserved.