A minisatellite polymorphism in intron III of the barramundi (Lates calcarifer) growth hormone gene.

This paper describes the detection of a polymorphism within the growth hormone (GH) gene of the fish barramundi (Lates calcarifer). PCR amplification of barramundi genomic DNA generated three different sized products: A, 409 bp; B, 478 bp; and H, 520 bp. Each barramundi isolate displayed one of four different types of profiles, which contained specific combinations of these PCR products. Sequence analysis confirmed that products A and B are different forms of the barramundi GH gene, and studies showed that product H was an artifact due to heteroduplex formation between the two smaller-sized molecules. The polymorphic nature of these PCR products was due to differences in the number of repeat monomers within the 5' end of the barramundi decaminisatellite, an AT-rich repetitive sequence that was identified within intron III of this gene. The barramundi decaminisatellite consisted of 24 or 28 10-nucleotide imperfect direct repeat monomers in a tandem array. The monomers were grouped into one of three different families and evidence for monomer homogenization by crossover fixation was presented. The barramundi decaminisatellite differed from previously reported AT- or GC-rich minisatellites, although a similar decaminisatellite has been identified in intron III of the tilapia GH gene.