Three synonymous genes encode calmodulin in a reptile, the Japanese tortoise, Clemmys japonica

Three distinct calmodulin (CaM)-encoding cDNAs were isolated from a reptile, the Japanese tortoise (Clemmys japonica), based on degenerative primer PCR. Because of synonymous codon usages, the deduced amino acid (aa) sequences were exactly the same in all three genes and identical to the aa sequence of vertebrate CaM. The three cDNAs, referred to as CaM-A, -B, and -C, seemed to belong to the same type as CaMI, CaMII, and CaMIII, respectively, based on their sequence identity with those of the mammalian cDNAs and the glutamate codon biases. Northern blot analysis detected CaM-A and -B as bands corresponding to 1.8 kb, with the most abundant levels in the brain and testis, while CaM-C was detected most abundantly in the brain as bands of 1.4 and 2.0 kb. Our results indicate that, in the tortoise, CaM protein is encoded by at least three non-allelic genes, and that the 'multigene-one protein' principle of CaM synthesis is applicable to all classes of vertebrates, from fishes to mammals.