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UBC Theses and Dissertations

The structure and evolution of the bovine prothrombin gene Irwin, David Michael


The gene for bovine prothrombin is 15.6 Kbp in length which encodes a mRNA of 2025 nucleotides plus a poly(A) tail. The prothrombin gene is composed of 14 exons separated by 13 introns, all of which vary in size. The positions of the introns found within the prothrombin gene provides some insight into the evolution of prothrombin and provide evidence on the origin of introns. Within the activation peptide and leader sequence of precursor prothrombin, some of the introns appear to separate structural and functional protein domains. Introns are found to separate certain domains, including the pre-peptide, the propeptide and Gla region, and each of the kringles. This organization of exons may reflect the evolution of the prothrombin gene as the result of the fusion of exon(s) containing protein domains by exon shuffling. The activation peptide appears to be constructed from four domains: a pre-peptide, a pro-peptide and Gla region, and two kringles. On comparison of the exon organization of the serine protease domain of prothrombin and other serine protease genes, it was found that none of the introns of the prothrombin gene are shared with any of the other serine protease genes. This absence of shared introns is in contrast to the shared introns found for the shared domains of the activation peptide and leader. The positions of the introns of the serine protease domain of serine proteases genes does not appear to reflect the evolution of the serine protease from protein domains, but rather the result of intron insertion into the serine protease coding regions. Intron insertion would also explain the origin of the few introns of the activation peptide that do not appear to separate protein domains. In conclusion, the organization of the exons and introns of the gene for prothrombin reflect both the origin of introns by insertion events, and the use of introns in exon shuffling. The insertion of introns, and the subsequent possibility of exon shuffling appear to have been essential for the evolution of the multidomainal proteins, such as prothrombin, which are essential for vertebrate life.

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