PRESENCE OF A GENE IN THE ARCHAEBACTERIUM METHANOCOCCUS-VANNIELII HOMOLOGOUS TO SECY OF EUBACTERIA

The nucleotide sequence of a gene located at the promoter-distal side of the 'spectinomycin-operon' homologue of the archaebacterium Methanococcus vannielii was determined. Its derived amino acid sequence displayed 20% (identical positions) or 52% (including conservative exchanges) similarity, respectively, to SECY from E coli. An alignment of the Methanococcus SECY with eubacterial SECY sequences showed the existence of 10 membrane-associated primary structure domains in equivalent positions. The 5' and 3' ends of the secY transcript were mapped and the gene was expressed in the T7 promoter/polymerase system in E coli. The temperature-sensitive growth of the E coli mutant IQ292 which harbours a secY(ts) mutation could be complemented by the secY gene from Methanococcus. This indicates that a protein integral to an archaebacterial ether-lipid membrane can be inserted into a eubacterial phospholipid membrane without apparent loss of function.