Primary structure of human coagulation factor XIII.

The complete primary structures of the a and b subunits of human factor XIII were determined by a combination of cDNA cloning and amino acid sequencing. The a subunit is composed of 731 amino acids including an activation peptide (37 amino acids), an active site (-Tyr-Gly-Gln-Cys-Glu-), a putative calcium binding site(s), and a thrombin-inactivation site. The functional regions of the a subunit appear to be located in separate exons of its gene. The b subunit consists of 641 amino acids including ten tandem repeats that are homologous with those in at least 13 other proteins. Each GP-I structure in the b subunit is probably encoded by a separate exon.