NUCLEOTIDE-SEQUENCE OF A PUTATIVE SUCCINATE-DEHYDROGENASE OPERON IN THERMOPLASMA-ACIDOPHILUM

28 amino acids from the N-terminal region of a putative terminal oxidase from the archaebacterium Thermoplasma acidophilum were determined by Edman degradation. On basis of this amino acid sequence a degenerated oligonucleotide was synthesized and used as a radioactive probe for Southern blot analysis of EcoRI digested genomic DNA. A 2.3 kb EcoRI fragment strongly hybridized to the probe and a size selected genomic library from genomic DNA was constructed. Several clones scored positive by screening the library with the degenerated oligonucleotide, from which only one clone contained a EcoRI DNA fragment encoding the 28 amino acid sequence determined by protein sequencing. Sequence analysis revealed the presence of three genes in the typical arrangement of an operon. The first gene codes for a protein containing 11 cystein residues in an arrangement typical for Fe/S proteins. Protein sequence comparison revealed significant homologies to the fumarate reductase and succinate dehydrogenase of other bacteria. The two other genes encode small hydrophobic proteins probably serving as membrane anchor for the Thermoplasma acidophilum succinate dehydrogenase.