Cloning of mitochondrial DNA from Paracentrotus lividus.  In order to study the gene organization and sequence of the mt DNA from sea urchin Paracentrotus lividus, we have cloned the two Bam HI fragments of 12 Kb and 4 Kb in the plasmid vectors pAT 153 and pBR 322 respectively. The cloning has been tested by hybridizing the DNA extracted from the recombinant plasmids with sea urchin mt DNA and by comparing the restriction patterns of the cloned fragments with those shown by fragment isolated from sea urchin mt DNA. This has allowed the determination of the size of sea urchin mt DNA that results to be about 15.000 base pairs, similar to that already reported for other animal mt DNA.