Structure of the human alpha 1-microglobulin-bikunin gene.

Alpha 1-Microglobulin (protein HC) and bikunin (formerly HI-30, urinary trypsin inhibitor, inhibitor subunit of inter-alpha-(trypsin) inhibitor) are abundant serum glycoproteins. They belong to two distinct protein families, the lipocalin family, a family of transport proteins for small hydrophobic molecules and the Kunitz-family of proteinase inhibitors. Mature alpha 1-microglobulin and bikunin result from a common precursor. Now we have isolated and sequenced the human gene coding for this precursor protein. The gene consists of 10 exons which span 1.3 kb and 9 introns with an aggregate length of about 16.5 kb. The largest intron (6.5 kb) separates exon 6 (coding for the C-terminal sequence of alpha 1-microglobulin) from exon 7 (coding for a linker peptide and the N-terminal peptide of bikunin). Repetitive DNA sequences of the Alu-type occur downstream of the polyadenylation site, within introns 4 and 6, and upstream of the putative promoter region which has been defined by sequence comparison and transcription start site determination. The gene also contains several sequence motifs reminiscent to known enhancer sequences.