MOLECULAR-CLONING AND SEQUENCING OF THE CDNA CODING FOR A CALCIUM-BINDING PROTEIN REGUCALCIN FROM RAT-LIVER

The cDNA of a Ca2+-binding protein regucalcin was cloned from a rat li ver cDNA library which was constructed in lambdaZAPII by immunoscreeni ng. Positive clones were obtained from which spar ned the region of in terest, and they gave a sequence of 1.7 kb by sequencing with the dide oxynucleotide method. Analysis of the sequence of the cloned cDNA show ed that the cDNA encoded the complete amino acid sequence of the reguc alcin molecule. Regucalcin was composed of 299 amino acid residues and its molecular weight was estimated to be 33,388 Da. The hydropathy pr ofile of regucalcin showed a highly hydrophilic character. The nucleot ide and amino acid sequences of regucalcin did not have statistically significant homology, as compared with the registered sequences which are found in the EMBL and GenBank databases containing several other C a2+-binding proteins (calmodulin, calbindin-D28k and S-100beta). The r egucalcin molecule did not contain the EF-hand motif as a Ca2+-binding domain. The present study demonstrates that regucalcin is a unique Ca 2+-binding protein in the liver of rats.