Structure and organization of a novel calmodulin gene of Arabidopsis thaliana.

The calcium binding protein calmodulin is involved in regulating various cellular and biochemical processes. A gene for calmodulin has been isolated from a genomic library of Arabidopsis thaliana constructed in lambda EMBL-4 using a heterologous cDNA probe from electric eel. The genomic clone was found to contain a complete copy of a distinct calmodulin (CaM) gene. A comparison of the nucleotide sequence with those from the other plant and animal systems reveals that the Arabidopsis CaM gene contains two exons and a single intron of 364 bp. The intron splits the triplet encoding the 25th amino acid of the protein. The Arabidopsis calmodulin protein appears to be distinct in containing a single amino acid substitution, arg to lys at the 126th position from the other known plant and animal calmodulins. The 5'-upstream region of this CaM gene (ACaM4) contains several known sequence-elements, a few of which are known to be implicated in transcriptional activation in response to light, U.V. radiation and heat shock besides the presence of many small multiple repeats. The Southern hybridization analysis and a comparison of nucleotide sequence with those of the other calmodulin genes of Arabidopsis indicate that the calmodulin gene, ACaM4, belongs to a small multigene family consisting of at least four members in the Arabidopsis genome.