CHROMOSOMAL ORGANIZATION AND NUCLEOTIDE-SEQUENCE OF THE GENES FOR ELONGATION-FACTORS EF-1-ALPHA AND EF-2 AND RIBOSOMAL-PROTEIN-S7 AND RIBOSOMAL-PROTEIN-S10 OF THE HYPERTHERMOPHILIC ARCHAEUM DESULFUROCOCCUS-MOBILIS

The Desulfurococcus mobilis genes fus (encoding EF-2) and tuf (for EF- 1 alpha) were cloned and sequenced together with genes for ribosomal p roteins S10 (rps10) and S7 (rps7). Unlike Methanococcus, which display s the bacterial-like fus and tuf gene context 5'-rps12-rps7-fus-tuf-3' , and similar to Sulfolobus and Pyrococcus, the Desulfurococcus fus ge ne (734 codons) has a distinct chromosomal location. Moreover, tuf (44 1 codons) is the promoter-proximal unit of a three-gene cluster compri sing the genes rps10 (98 codons) and tRNA(Ser); the arrangement of the cluster is 5'-tuf - 91 bp spacer - rps10 - 138 bp spacer - tRNA(Ser)- 3' and the tuf gene is preceded by a canonical archaeal promoter. The D. mobilis gene rps7 (198 codons) is located further upstream from tuf (535 bp 'silent' intergenic spacing) and no rps12 homolog occurs in i ts immediate vicinity. Also, judging from putative promoter and transc ription termination sequences, rps7 appears to be separately transcrib ed. Analysis of the predicted fus and tuf gene products revealed the t hree consensus motifs characteristic of GTP-binding proteins, and the fus-encoded EF-2 protein also displayed the consensus sequence require d for ADP-ribosylation by Diphtheria toxin. Both EF sequences were def initely crenarchaeal by comparison with available homologs from other Archaea. Outgroup-rooted phylogenies derived from the sequences of rib osomal proteins S10 and S7 yielded the Sulfolobus-Desulfurococcus asso ciation at a high bootstrap confidence