Conservation of the 3'-untranslated regions of calmodulin mRNAs in cetaceans

Three separate calmodulin (CaM) genes (I, II and III) encoding an identical CaM protein but differing in the 5'- and 3'-untranslated regions of each of the three mRNAs are present and highly conserved in all mammals (so far examined). Primers complementary to the 3'- untranslated region (3'UTR) of each of the three mRNAs occurring in human, rat and mouse were synthesized and used to amplify regions of the 3'UTR from genomic DNA isolated from cetaceans, specifically from the bottled-nosed dolphin (Tursiops truncates), the pygmy sperm whale (Kogia breviceps) and the humpback whale (Megaptera novaeangliae). Using several primers and PCR conditions, the three CaM genes were identified in all three species by this method with one exception. The sequenced regions of the 3'UTRs of the three genes of the cetaceans exhibited a high percentage identity when compared to the corresponding regions of these three CaM mRNAs isolated from humans (85-96%). These partial sequences of the 3'UTR regions and the corresponding regions for humans, rats and mice that were available from the database were aligned and a phylogenetic tree was constructed. The three CaM genes from all species showed a close phylogenetic relationship based on these 3'UTR sequences. Such high conservation of the 3'UTRs suggests a specialized and significant function for this region in mammals.