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

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, Arothron 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(acetate-mercurimethyl) dioxane], showed that A. diadematus DNA can be resolved into several components, characterized by buoyant densities of 1.700, 1.7045, 1.708, 1.712 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. [ABSTRACT FROM AUTHOR]