The rat vitamin D binding protein (Gc-globulin) gene. Structural analysis, functional and evolutionary correlations.

The complete rat vitamin D binding protein (DBP) gene has been cloned and characterized. Genomic mapping suggests that there is only one copy of this gene in the haploid genome. The gene spans 35 kilobase pairs and contains 13 exons. All exons, exon/intron borders, and 2196 base pairs of 5'-flanking region have been sequenced. The transcription cap site, determined by primer extension analysis, is 62 base pairs upstream from the start of translation and predicts that an unusual TGTAAA motif may serve as a surrogate TATA. The promoter region contains about 50% nucleotide sequence similarity to the corresponding region of the partially characterized human DBP gene and is uniquely interrupted by a repetitive element. Although lacking in overall sequence similarity to the albumin (ALB) and alpha-fetoprotein (AFP) genes, the 5'-flanking region of the DBP gene contains a number of conserved segments which may correspond to critical proximal promoter elements in this gene family. The location of the introns in the coding region of the DBP gene is highly conserved when compared with the ALB and AFP genes. Detailed comparison of exon size and content confirms the previous prediction that the smaller size of the DBP protein results from loss of internal exons 12 and 13 from the DBP progenitor gene during its evolutionary divergence from ALB and AFP.