Organization of the human alpha 2-plasmin inhibitor gene.
We have isolated overlapping phage genomic clones covering an area of 26 kilobases that encodes the human alpha 2-plasmin inhibitor. The alpha 2-plasmin inhibitor gene contains 10 exons and 9 introns distributed over approximately 16 kilobases of DNA. To our knowledge, the number of introns is the highest yet reported for a member of the serine protease inhibitor (serpin) superfamily. All introns are located in the 5'-half of the corresponding mRNA. The 5'-untranslated region and the leader sequence are interrupted by 3 introns totaling approximately equal to 6 kilobases. A "TATA box" sequence is located 17 nucleotides upstream from the proposed transcription initiation site. Multiple "GC box" sequences, G + C-rich sequences, and "CCAAT box"-like sequence, the hepatitis B virus enhancer element-like sequence and the human immunodeficiency virus enhancer-like sequence appear in the 5'-flanking region. The NH2-terminal region, which implements factor XIII-catalyzed cross-linking of alpha 2-plasmin inhibitor to fibrin, is encoded by the 4th exon. The reactive site and plasminogen-binding site, both located in the COOH-terminal region, are encoded by the 10th exon. When similar amino acids of alpha 2-plasmin inhibitor and other members of the serpin gene superfamily are aligned, the position of the 7th intron of the alpha 2-plasmin inhibitor gene aligns precisely with that of the second intron of the genes for rat angiotensinogen and human alpha 1-antitrypsin genes and is misaligned by only one nucleotide with that of the third intron of antithrombin III, suggesting that the alpha 2-plasmin inhibitor gene originates from the common ancestor of these serine protease inhibitors.