The human bone sialoprotein gene (IBSP): genomic localization and characterization.

We have isolated and partially sequenced the human bone sialoprotein gene (IBSP). IBSP has been sublocalized by in situ hybridization to chromosome 4q28-q31 and is composed of six small exons (51 to 159 bp) and 1 large exon (approximately 2.6 kb). The intron/exon junctions defined by sequence analysis are of class O, retaining an intact coding triplet. Sequence analysis of the 5' upstream region revealed a TATAA (nucleotides -30 to -25 from the transcriptional start point) and a CCAAT (nucleotides -56 to -52) box, both in the reverse orientation. Intron 1 contains interesting structural elements composed of polypyrimidine repeats followed by a poly(AC)n tract. Both types of structural elements have been detected in promoter regions of other genes and have been implicated in transcriptional regulation. Several differences between the previously published cDNA sequence (L. W. Fisher et al., 1990, J. Biol. Chem. 265, 2347-2351) and our sequence have been identified, most of which are contained within the untranslated exon 1. Three base revisions in the coding region include a G to T (Gly to Val, amino acid 195), T to C (Val to Ala, amino acid 268), and T to A (Glu to Asp, amino acid 270). In conclusion, the genomic organization and potential regulatory elements of human IBSP have been elucidated.