Nucleotide sequence organization in the very small genome of a tetraodontid fish, Arothron diadematus.

We have investigated the sequence organization of the very small genome (DNA content/haploid cell c = 0.4-0.5 pg) of a tetraodontid fish, Arotron diadematus, by using two main experimental approaches. The first one, renaturation kinetics, showed that slowly reassociating, intermediate, fast and foldback sequences represented 87%, 7%, 5% and 1%, respectively, of A. diadematus DNA, which is, so far, the vertebrate DNA lowest in repeated sequences. The second approach, centrifugation in Cs2SO4/BAMD density gradients [BAMD = bis(acetatomercurimethyl)dioxane], showed that A. diadematus DNA can be resolved into several components, characterized by buoyant densities of 1.700, 1.704(5), 1.708, 1.702 and 1.723 g/cm3, and representing 15%, 73%, 4%, 4% and 2.5%, respectively, of total DNA. The last component comprised a satellite DNA and ribosomal DNA. A family of interspersed repeats, possibly related to the AluI family of warm-blooded vertebrates, showed an extremely specific genomic distribution, being present in only the 1.708 g/cm3 component, which it matched in base composition.