Evolutionary origin of thyroglobulin by duplication of esterase gene.

Rat liver microsomal carboxyesterase E1 was found to have homology with five esterases and with the COOH-terminal parts of two thyroglobulins. A phylogenetic tree constructed for these proteins shows that this new superfamily has evolved from a common ancestral gene that encoded a carboxyesterase. The tree also shows that the ancestral gene already existed before the divergence of vertebrates and invertebrates and later its duplicated genes gained various kinds of esterase activity. According to the tree, one of the duplicated genes evolved into the COOH-terminal half of thyroglobulin by a gene fusion with a DNA sequence whose evolutionary origin is unknown.