Putative amino acid sequence of chick calcium-binding protein deduced from a complementary DNA sequence

Abstract

Two DNA fragments coding for chick CaBP have been isolated and sequenced. cDNA was prepared from enriched intestinal mRNA and cloned in pUC12. The recombinant clones were screened by differential hybridisation with 32P-cDNA probes synthesized from vitamin D replete and deficient chick intestinal mRNA. Two clones had outstanding affinity with the +D probe. Hybrid-arrested and hybrid-selected translation systems showed that both clones hybridised to mRNA coding for immunoprecipitable CaBP. The mRNA for CaBP has a 100 bp G,C rich sequence before a 786 bp coding region followed by 1250 nucleotides 3' untranslated region. Nucleotides coding for the Ca-binding sites show a high degree of homology for Ca-binding sites in chick calmodulin and rat intestinal CaBP. The amino acid sequence specified by the longest open reading frame contains five Ca-binding sites but is too large for the native CaBP; post-translational modification must therefore occur.