The mitochondrial Pylaiella littoralis nad11 gene contains only the N-terminal FeS-binding domain

We describe a nad11 gene located on the mitochondrial genome of the brown a lga Pylaiella littoralis. This gene is cotranscribed with other neighbourin g nad genes. It encodes the first domain only of the Nad11 polypeptide, i.e . a 23-kDa, FeS-binding domain instead of the usual 75/80-kDa protein found in the mitochondrial or alpha-proteobacterial complex I enzymes. The secon d domain of the protein, of unknown function, seems to be entirely missing in this alga. Cyanobacteria, beta-proteobacteria and actinomycetes also fea ture small homologous genes, known as hoxU, and it has been suggested that these could function in complex I of cyanobacteria. These observations indi cate that complex I can probably function with the first domain only of the 75-kDa protein. P. littoralis represents the first such example within the alpha-proteobacterial/mitochondrial lineage. (C) 1999 Elsevier Science B.V . All rights reserved.