Immunoselection of cDNAs to Avian Intestinal Calcium Binding Protein 28K and a Novel Calmodulin-like Protein: Assessment of mRNA Regulation by the Vitamin D Hormone

Calcium’s role in a variety of cellular processes has been well documented. The storage, distribution, and delivery of calcium are regulated by a family of binding proteins including troponin C, calmodulin, parvalbumin, and vitamin D dependent calcium binding protein (CaBP-28), all of which have evolved from a common ancestral gene. To evaluate vitamin D regulation of gene transcription, a CaBP-28 cDNA (767 base pairs) was isolated from a chicken intesting λgt11 library utilizing a polyvalent CaBP-28 antibody as a probe. Coincident with the identification of the CaBP-28 cDNA, a group of cDNAs also was isolated (with the anti-CaBP-28 antibody) that demonstrated 84% nucleotide homology and 99% deduced amino acid homology with chicken brain calmodulin (CaM). This new CaM-like cDNA was named neoCaM. There is little nucleotide homology between the CaBP-28 cDNA and neoCaM. The CaBP-28 cDNA hybridizes with three transcripts of 2000, 2900, and 3300 bases which are dramatically induced by 1,25-dihydroxyvitamin D₃[1,25(OH)₂D₃], while the neoCaM cDNA recognizes three distinct (from CaBP-28) transcripts. Two of these mRNAs are 1400 and 1800 bases as described for brain CaM, but another larger 4000-base transcript is detected with neoCaM. Neither the CaM nor the neoCaM transcript reveals any modulation by 1,25(OH)₂D₃. Herein, we discuss the possible significance of not only the isolation of both cDNAs with a single antibody but also the relation of neoCaM to other well-characterized CaM cDNAs.