gamma and gamma' chains of human fibrinogen are produced by alternative mRNA processing.

cDNAs and the genomic DNA coding for the gamma and gamma' chains of human fibrinogen have been isolated and characterized by sequence analysis. The cDNAs coding for the gamma and gamma' chains share a common nucleotide sequence coding for the first 407 amino acid residues in each polypeptide chain. The predominant gamma chain contains an additional four amino acids on its carboxyl-terminal end (residues 408-411). These four amino acids, together with the 3' noncoding sequences, are encoded by the tenth exon. Removal of the ninth intervening sequence following the processing and polyadenylation reactions yields a mature mRNA coding for the predominant gamma chain. The less prevalent gamma' chain contains 20 amino acids at its carboxyl-terminal end (residues 408-417). These 20 amino acids are encoded by the immediate 5' end of the ninth intervening sequence. This results from an occasional processing and polyadenylation reaction that occurs within the region normally constituting the ninth intervening sequence. Accordingly, the gene for the gamma chain of human fibrinogen gives rise to two mRNAs that differ in sequence on their 3' ends. These mRNAs code for polypeptide chains with different carboxyl-terminal sequences. Both of these polypeptides are incorporated into the fibrinogen molecule present in plasma.