Cloning, characterization and chromosomal location of a satellite DNA from the Pacific oyster, Crassostrea gigas

We report the cloning and characterization of a high-copy-number, tandem-repeat satellite DNA sequence from the genome of the Pacific oyster, Crassostrea gigas (Cg). The monomeric unit was found to be 166 (+/- 2) bp in length with 79-94% homology between monomers of the array. The sequence is Af T-rich (60%) and lacks internal repetition and substructural features. The repeat was estimated to account for 1-4% of the Cg genome. Fluorescence in situ hybridization (FISH) studies mapped the repeat to two distinct heterochromatic regions of two pairs of homologous chromosomes on Cg embryonic metaphases. Also, the number of metaphase chromosomes containing this repeat varied with the ploidy of the cell.