[Structure, expression and control of calbindins-D].

The Calbindins-D (CaBP9K and 28K), like calmodulin, belong to a group of intracellular proteins that bind calcium with high affinity. Each protein is encoded by a separate gene and there is no direct filiation between the two genes. We have demonstrated the tissue-specific expression and regulation of CaBP9K gene. This gene is expressed in the intestine, placenta and uterus of the rat as a single 0.5kb long transcript. Exogenous 1,25(OH)2D3 triggers the rapid synthesis of CaBP9K mRNA and accumulation of translatable CaBP9K mRNA in the duodenum of vitamin D-deficient rats. Calcium also stimulates CaBP9K gene expression in this tissue. In contrast 1,25(OH)2D3 does not change the uterine concentration of CaBP9K but estrogen stimulates the transcription of the CaBP9K gene in the uterus. The promoter region of rat CaBP9K gene contains 1 TATA box and 4 CAAT box-type sequences and several steroid hormone regulatory elements. The CaBP9K gene is therefore a suitable model for studying the tissue-specific regulation of gene expression by steroid hormones.