The complete sequence of a brown algal mitochondrial genome, the ectocarpale Pylaiella littoralis (L.) Kjellm.

We describe here the complete sequence (58,507 bp) of the mitochondrial gen ome of the brown alga Pylaiella littoralis (Ectocarpales). This molecule di splays an AT content of 62.0% and contains seventy-nine genes, most of them (73) encoded on one strand. They include the usual mitochondrial set of pr otist genes and a number of rarer genes. Among these, several ribosomal pro tein genes and the rn5 were identified. Twenty-four tRNA genes are present in this genome, insufficient to decode all genes. The other conspicuous fea tures of this molecule are: a large (3018 nucleotides) in-frame insertion o f unknown function in the cox2 gene; the presence of two different lineages of group II introns, including complete reverse transcriptase-like genes, one in the cox1 and the other in the mi gene; the concomitant occurrence of a T7-like RNA polymerase and of several well-conserved a-proteobacterial-t ype promoters; and a small nad11 gene, coding for the first domain only of this NADH dehydrogenase subunit. Altogether, the mitochondrial genome of P. littoralis exhibits both ol-proteobacterial characteristics and evidences of the independent integration of several exogenous DNA fragments.