Structure of the human gamma-fibrinogen gene. Alternate mRNA splicing near the 3' end of the gene produces gamma A and gamma B forms of gamma-fibrinogen.

The gamma chain of human fibrinogen exists in 2 nonallelic forms, gamma A and gamma B, which differ only in their carboxyl termini. We have found that only one genomic locus exists for gamma-fibrinogen and that the gamma A and gamma B chains arise by alternate mRNA splicing near the 3' end of this gene. In contrast to the rat gamma B mRNA which is produced by alternate splicing with identical polyadenylation sites, human gamma B is produced when the eighth intervening sequence remains unspliced and a polyadenylation signal within this intron is used. The new carboxyl terminus is 16 amino acids longer than the gamma A protein, and although there is only minimal homology between the rat and human carboxyl termini they share a very high proportion of acidic amino acids.