Multiple calmodulin genes in fish

In mammals, identical calmodulin (CaM) proteins are encoded by three nonallelic genes that differ in their promoter regions and untranslated regions (UTRs). The UTRs of each of these three genes are specific for each gene and are highly conserved. In this study, sequences obtained from the GenBank and EST databases and sequencing were examined for several species of fish to ascertain whether this multi-gene one protein system exhibited in mammals extends to other vertebrates. Three genes in zebrafish (Danio rerio) designated alpha, beta, and gamma were identified. As in mammals, these genes differ in the 3'-UTR region but encode completely identical CaMs. PCR primers spanning the coding and the 3'-UTR regions were designed based on the assembled sequences and used to confirm the presence of each gene in the cDNA library. Other species of fish were also found to contain homologous genes that were closely related as indicated by phylogenetic analysis. The 3'-UTR of the alpha, beta and particularly the gamma CaM gene of fish were not found to be as conserved as the corresponding genes of mammalian species possibly due to the span of evolutionary time. Only a few short elements in the 3'-UTR were observed to be similar in fish and mammals. These short regions of identity are shared primarily between the mammalian CaM II and CaM I and the alpha gene and beta gene of fish, respectively. Thus, the multi-gene one protein system occurs among fish as well as among mammals.