CHARACTERIZATION OF THE HUMAN CALM2 CALMODULIN GENE AND COMPARISON OFTHE TRANSCRIPTIONAL ACTIVITY OF CALM1, CALM2 AND CALM3

Human calmodulin is encoded by three genes CALM1, CALM2 and CALM3 loca ted on different chromosomes. To complete the characterization of this family, the exon-intron structure of CALM2 was solved by a combinatio n of genomic DNA library screening and genomic PCR amplification. Intr on interruptions were found at identical positions in human CALM2 as i n CALM1 and CALM3, however, the overall size of CALM2 (16 kb) was almo st twice that of the other two human CALM genes. Over 1 kb of the 5' f lanking sequence of human CALM2 were determined, revealing the presenc e of a TATA-like sequence 27 nucleotides upstream of the transcription al start site and several conserved sequence elements possibly involve d in the regulation of this gene. To determine if differential transcr iptional activity plays a major role in regulating cellular calmodulin levels, we directly measured and compared the mRNA abundance and tran scriptional activity of the three CALM genes in proliferating human te ratoma cells. CALM3 was at least 5-fold more actively transcribed than CALM1 or CALM2. CALM transcriptional activity agreed well with the mR NA abundance profile in the teratoma cells. In transient transfections using luciferase reporter genes driven by 1 kb of the 5' flanking DNA of the three CALM genes, the promoter activity correlated with the en dogenous CALM transcriptional activity, but only when the 5' untransla ted regions were included in the constructs. We conclude that the CALM gene family is differentially active at the transcriptional level in teratoma cells and that the 5' untranslated regions are necessary to r ecover full promoter activation, The sequence data reported in this pa per have been submitted to the GenBank Data Library under the accessio n numbers U94725, U94726, U94727, and U94728.