The single calmodulin gene of the cephalochordate Branchiostoma

The cDNA and gene for calmodulin (CaM) from the cephalochordate Branchiostoma were isolated and characterized. The nucleotide sequence of the Branchiostoma CaM cDNA is about 80% identical to the CaM of Drosophila and Aplysia. However, all nucleotide substitutions are silent, therefore the amino acid sequences of all these CaMs are identical. Branchiostoma and Aplysia CaM genes have the same exon/intron organization. PCR, Northern and genomic Southern analyses showed that Branchiostoma CaM is encoded by a single copy gene, while fish are known to have at least four CaM genes. These results fit the hypothesis that major gene duplication events occurred close to the origin of vertebrates, i.e., after the divergence of the cephalochordate lineage.