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

Kouji Shimoda,Jun Kimura,Taiji Miyake ,Kensaku Maejima

doi:10.1590/s1415-47572002000100009

Abstract

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.

Highlights

Calmodulin (CaM), a prototype of EF-hand Ca2+-binding protein, is ubiquitously distributed in all eukaryotic cells, and is abundant in the brain and testes of mammals (Kakiuchi et al, 1982)
The results indicate that reptiles possess three active CaM genes, corresponding to CaMI, CaMII, and CaMIII, respectively, and the ‘multigene-one protein’ principle of CaM synthesis is as applicable to reptiles as it is to other vertebrates
The nt sequence homologies between any two of the three types of CaM cDNA are very low, considering that the aa sequence of CaM protein is identical in all vertebrates

Summary

Introduction

Calmodulin (CaM), a prototype of EF-hand Ca2+-binding protein, is ubiquitously distributed in all eukaryotic cells, and is abundant in the brain and testes of mammals (Kakiuchi et al, 1982). When CaM binds to the Ca2+ ion, the protein becomes active, and it in turn activates many other enzymes. It plays a pivotal role as a cofactor regulating a wide variety of calcium-dependent proteins. The reason for the presence of multiple synonymous genes in animals is unclear, differences in the 5’ and 3’ non-coding region of the rat CaM genes suggest that each gene may be differentially regulated. The results indicate that reptiles possess three active CaM genes, corresponding to CaMI, CaMII, and CaMIII, respectively, and the ‘multigene-one protein’ principle of CaM synthesis is as applicable to reptiles as it is to other vertebrates

Methods

Results

Conclusion