Sequence of rat intestinal vitamin D-dependent calcium-binding protein derived from a cDNA clone. Evolutionary implications (original) (raw)

We have recently reported molecular cloning of the cDNA synthesized from rat duodenal mRNA-encoding intestinal calcium-binding protein (ICaBP), a vitamin D3-induced protein (Desplan, C., Thomasset, M., and Moukhtar, M. S. (1983) J. Biol. Chem. 258, 2762-2765). Nucleotide sequence analysis of the longest cDNA insert (375 base pairs) permitted the assignment of 207 nucleotides of the coding region and 104 nucleotides of the entire 3'-noncoding region of the mRNA. Although the derived amino acid sequence for rat ICaBP differed from the bovine and porcine sequences by 16 and 14 residues, respectively, all the residues of each calcium-binding site met the proposed requirements of the "EF hand" theory. In contrast, several differences found in the linker regions might explain the absence of cross-immunoreactivity between rat and porcine ICaBPs. Analysis of nucleotide sequence homologies between the coding and noncoding regions showed that the region coding for the two calcium-binding sites (I and 11) was immediately followed in the noncoding region by a sequence very similar to the sequence coding for site I. This suggests that rat ICaBP mRNA contains the remains of an untranslated calcium-binding site 111-like structure and that low M, ICaBP could result in early termination of the translation of a larger molecule containing four sites. Vitamin D-dependent CaBPs' (Wasserman and Taylor, 1966; Wasserman et al., 1978) belong to the large family of intracellular proteins which bind calcium with affinity constants in the range 10-s-10-5 M (Kretsinger, 1976). Based upon the number of their calcium-binding sites, two classes of such vitamin D-dependent proteins have been identified in mammals. A M , = 28,000 molecule found in kidney and cerebellum has four calcium-binding sites, whereas a M , =