THE HUMAN INTEGRIN BETA(3) GENE IS 63 KB AND CONTAINS A 5'-UTR SEQUENCE REGULATING EXPRESSION

The human blood platelet fibrinogen receptor, integrin alpha(IIb)beta( 3) (glycoprotein IIb-IIIa) is an archetypal member of the integrin fam ily of adhesive molecules and is the only integrin encoded by genes ph ysically linked in the genome. Because studies on the normal and abnor mal expression of any gene require a thorough understanding of its org anization, the initial goals of the current study were to determine th e size and complete the genomic organization for the beta(3) gene. We now report the isolation of the entire beta(3) gene in a single P1 pla smid and for the first time have linked the first and second exons on a contiguous fragment of DNA. Using pulsed-field gel analysis, we dete rmined the full size of the beta(3) gene to be 63 kb and show a large (16.7 kb) first intron; based on this information, we propose a unifor m numbering system for the beta(3) exons. We have completed the 5' gen omic structure and generated a long-range restriction map. The promote r and the 5' end of the first intron were found to have approximately 50% sequence identity with a region of the avian beta(3) gene known to possess functional transcriptional activity. Analysis of three differ ent homologous regions led to the identification of a sequence in the 5'-UTR of the human gene, CCGCGGGAGG, which shares 90% identity with t he avian gene and which bound nuclear proteins in DNasel and electroph oretic mobility shift assay studies. Mutating this sequence caused a 2 .6-fold reduction in reporter gene activity. In these studies we have (1) determined the full length and 5' organization of the beta(3) gene , (2) identified a large region of homology between the 5' regions of the avian and human genes, and (3) identified a sequence in the 5'-UTR that augments gene expression. Knowing the genomic structure of beta( 3) has permitted the uncovering of new mechanisms of mutagenesis causi ng Glanzmann thrombasthenia (Jin et al, J Clin Invest 98:1745, 1996), and our findings will be valuable for such genetic analyses as well as for studies on the transcriptional regulation of beta(3) and other in tegrin genes. (C) 1997 by The American Society of Hematology.