Cloning and characterization of a cDNA for the B beta chain of rat fibrinogen: evolutionary conservation of translated and 3'-untranslated sequences.

A cDNA clone for the B beta chain of rat fibrinogen has been isolated and characterized. The cDNA insert is 1023 bp in length and corresponds to the 3' half of the B beta chain mRNA. The cDNA represents 890 bp of the coding sequence for the C-terminal half of the B beta chain and 133 bp of the 3'-untranslated region. The coding sequence for this region of the rat cDNA shares a high degree of identity with the corresponding regions of the human and bovine B beta-chain cDNAs and a moderate degree of identity with the corresponding region of the lamprey B beta-chain cDNA. A comparison of the amino acid sequences deduced from these cDNAs reveals three regions which share extensive identity among all four sequences. Two additional regions are identified which share extensive identity among the three mammalian sequences and significant identity with the lamprey sequence. These regions appear to represent distinct functional domains. Possible functions for these domains are briefly discussed. A high degree of identity also exists between the 3'-untranslated regions of the three mammalian cDNAs, suggesting that this region of the mRNA, although noncoding, is functionally important.