Organization and nucleotide sequence of a transcriptional unit ofMethanococcus vannielii comprising genes for protein synthesis elongation factors and ribosomal proteins

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Abstract
By a chromosome walking strategy the DNA region fromMethanococcus vannielii flanking the genes for protein synthesis elongation factor (EF) 1α and EF-2 was cloned and sequenced. A gene organization of 5′-β′-open reading frame (ORF) 1-ORF2-S12-S7-EF-2-EF-1α-S10-ORF3-ORF4-3′ was found where β′, S12, S7, S10, EF-2, and EF-1α represent gene products with sequences similar to the β′ subunit of RNA polymerase, ribosomal proteins S12, S7, and S10, and EF-G and EF-Tu fromEscherichia coli, respectively. ORF1-4 represent gene products with no known eubacterial counterparts. Northern blot analysis of transcripts and nuclease S1 mapping showed that transcription initiates between β′ and ORF1 and terminates at the 3′ side of the S10 gene and that the genes from ORF1 to S10 are contranscribed. Apart from the presence of two additional ORFs, ORF1 and ORF2, and of the gene for S10, this organization is identical to that of the eubacterial “streptomycin operon.” ORF1 displays sequence similarity to rat liver ribosomal protein L30 and may represent one of the “additional” ribosomal proteins ofMethanococcus. The sequenced part of the β′ gene and the EF-2 and EF-1α gene products fromMethanococcus, are more similar to their eukaryotic than to their eubacterial counterparts. It appears, therefore, that the genetic organization of the translational components resembles the situation in eubacteria, whereas their primary structures are more eukaryotic in nature.