Primary‐structural and evolutionary analyses of the growth‐hormone gene from grass carp (Ctenopharyngodon idellus)

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Abstract
The growth‐hormone (GH) gene of grass carp, one of the fastest‐growing species of farmed fish, was isolated and the DNA sequenced. Only one GH gene is found in this species. This gene, which is 2.5 kb in length, has five exons and four introns, in common with all of the mammalian and the recently published common‐carp GH genes. In the course of vertebrate evolution, the total lengthsof the intron and the non‐coding region of exon 5 of the GH gene have been shortened by 40–70%, whereas the encoding exons of the gene have been slightly increased. The more closely related species exhibit the closest sequence similarity in their GH genes. For example, the similarity of the exons is 84.1–93.2% between grass carp and common carp (within the same family of Syprinedae), 43.5–82.1% between grass carp and rainbow trout (in different orders of Teleostei) and 45.8–58.6% between glass carp and rat (in different grades of Vertebrata). In addition, similar DNA domains, such as thyroid‐hormone–receptor‐complex‐binding site and cell‐type‐specificciselements involved in regulation of expression of rat and human GH genes, have been localized in the corresponding regions of the grass‐carp GH gene.