Characterization of a complementary deoxyribonucleic acid coding for the alpha chain of human fibrinogen

A human liver cDNA library was screened for the alpha chain of fibrinogen with a cDNA clone from the corresponding bovine molecule as a hybridization probe. Several human clones coding for the alpha chain were identified, and one of these was used to rescreen the entire cDNA library of 18 000 recombinants. Plasmids with the largest cDNAs were isolated, and their inserts were sequenced. The largest cDNA insert contained 2224 base pairs, including a noncoding region at the 5'-end followed by a region coding for a signal peptide of 19 (or 16) amino acids and a mature protein of 625 amino acids, a stop codon of TAG, another noncoding region, and a poly(A) tail at the 3'-end. Eight tandem repeats of 39 base pairs were observed starting with nucleotide 905 (amino acid residue 270) and ending with nucleotide 1213 (amino acid residue 372). The identity in the nucleotide sequence in the tandem repeats ranged from 72 to 95% when compared to a consensus sequence. The predicted amino acid sequence for the mature polypeptide chain was 15 amino acids longer at the carboxyl-terminal end than that of the alpha chain isolated and sequenced from plasma fibrinogen. This indicates that minor proteolysis has taken place on the carboxyl-terminal end of the alpha chains, and this modification has probably occurred during secretion or circulation of the protein in plasma.