cDNA and amino-acid sequences and organization of the gene encoding the B beta subunit of fibrinogen from Xenopus laevis.

ABSTRACT

Fibrinogen, the major blood-clotting protein, is made up of three chains, A alpha, B beta and gamma, which are synthesized and secreted by the liver. In this communication, we describe the complete cDNA sequence, deduced amino acid (aa) sequence and organization of the gene encoding the B beta subunit of fibrinogen from Xenopus laevis (Xl). The cDNA representing the predominant form of the B beta mRNA comprises 2390 nucleotides (nt), with an open reading frame of 1467 nt coding for a 488-aa protein. The percent identity between Xl B beta and that of other animals ranges from 50% for lamprey to 66% for human. The Xl B beta gene consists of nine exons, one more than found in the human gene. The exon/intron boundaries in the frog and human B beta genes are in exactly conserved positions, except for junctions in the highly variable fibrinopeptide-encoding regions. Three of the exon/intron boundaries in the Xl B beta gene are also analogous to ones in A alpha and gamma genes of other species, supporting the notion of a close evolutionary relationship between the genes for all three subunits. This analysis of B beta from an amphibian provides the first complete description of the arrangement of exons and introns in any fibrinogen subunit gene from a non mammal and gives insight into the most highly conserved aspects of fibrinogen protein structure and gene organization.