Multiple calmodulin mRNA species are derived from two distinct genes.

Abstract

We have observed three calmodulin mRNA species in rat tissues. In order to know from how many expressed genes they are derived, we have investigated the genomic organization of calmodulin genes in the rat genome. From a rat brain cDNA library, we obtained two kinds of cDNAs (pRCM1 and pRCM3) encoding authentic calmodulin. DNA sequence analysis of these cDNA clones revealed substitutions of nucleotides at 73 positions of 450 nucleotides in the coding region, although the amino acid sequences of these calmodulins are exactly the same. DNA sequences in the 5' and 3' noncoding regions are quite different between these two cDNAs. From these results, we conclude that they are derived from two distinct bona fide calmodulin genes, CaMI (pRCM1) and CaMII (pRCM3). Total genomic Southern hybridization suggested four distinct calmodulin-related genes in the rat genome. By cloning and sequencing the calmodulin-related genes from rat genomic libraries, we demonstrated that the other two genes are processed pseudogenes generated from the CaMI (XSC9) and CaMII (ASC8) genes, respectively, through an mRNA-mediated process of insertions. Northern blotting showed that the CaMI gene is transcribed in liver, muscle, and brain in similar amounts, whereas the CaMU gene is transcribed mainly in brain. Si nuclease mapping indicated that the CaMI gene produced two mRNA species (1.7 and 4 kilobases), whereas the CaMII gene expressed a single mRNA species (1.4 kilobases).Calmodulin, a monomeric Ca2l-binding protein, mediates intracellular calcium interactions by regulating a variety of important enzyme systems through a calcium-calmodulin complex (12,17). It is reported that increases in the intracellular calmodulin concentration are coupled to the G1-S transition of the cell cycle (3) and that calmodulin may play a regulatory role in the reentry of quiescent (Go) cells into the cell cycle (5). The anticalmodulin drug (W13) specifically and reversibly inhibited the progression of cells into the S phase and DNA synthesis (4). These results suggest an important role for calmodulin in the regulation of cell cycle progression and DNA synthesis.The multifunctional roles of calmodulins in the cell through the regulation of calcium interactions with a variety of fundamental enzymes poses a question of how many expressed calmodulin genes exist in the cell. To answer this question, we have investigated the number of expressed calmodulin genes in the rat genome. Here, we report the existence of two kinds of bona fide calmodulin genes in the rat genome which generate at least three kinds of mRNAs species of different sizes. MATERIALS AND METHODSCloning and sequencing of cDNA (pRCM3) and a processed gene (XSC8). Construction of a rat (spontaneously hypertensive rat) genomic library and screening of a processed gene (XSC8) were described before (20). The rat (SpragueDawley) brain cDNA library, a generous gift from Hiroto Okayama (21), was screened with two kinds of probes according to the method of Hanahan and Meselson (10). One probe consisted of the S...

Down-regulation of a calmodulin-related gene during transformation of human mammary epithelial cells.

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

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