Structure of the human chromosomal gene for the 25 kilodalton insulin-like growth factor binding protein.

We have characterized the structure of the human chromosomal gene for the 25 kilodalton insulin-like growth factor binding protein (BP-25) as a first step toward understanding both the factors which regulate BP-25 transcription and also the evolution of the insulin-like growth factor binding proteins. The BP-25 gene is present in the human genome as a single copy which spans 5.2 kilobases and contains four exons. Primer extension localizes the mRNA cap site 165 base pairs (bp) upstream of the ATG translational start codon. Preliminary analysis of the putative promoter region for BP-25 demonstrates characteristics consistent with those of many eukaryotic promoters; these include a consensus TATA box beginning 28 bp 5' to the cap site and a consensus CCAAT promoter element beginning 72 bp upstream from the cap site.