Genomic structure and sequence of the gilthead seabream (Sparus aurata) growth hormone-encoding gene: Identification of minisatellite polymorphism inintron I

The growth hormone (GH) gene of the gilthead seabream (Sparus aurata) (saGH ) has been cloned, sequenced, and characterized. The saGH gene spans approx imately 4.3 kb and consists of six exons and five introns, as found for all cloned teleost GH genes with the exception of carps and catfish. The first and third introns contain long stretches of repetitive tandem repeats. The second intron, which is unusually long compared with that in other teleost s (and other vertebrates) spans 1747 nucleotides (nt) and contains several inverted repeats. Intron-targeted polymerase chain reaction (PCR) analysis identified length polymorphism of the first intron. Sequence analysis of fo ur variants (405, 424, 636, and 720 nt) out of many variants found revealed that the variation in length is due to differences in the number of repeat monomers (17-mer or 15-mer) as well as minor changes in their length. This repeat unit contains the consensus half-site motif of the thyroid hormone response element (TRE) and estrogen response element (ERE). Polymorphism wa s found also in the third intron. This is the first report of such high pol ymorphism of the first intron of GH gene in a vertebrate.