The gene encoding the 7S RNA of the archaebacterium Methanococcus voltae has been isolated. The gene occurs as a single copy within the genome and encodes an RNA molecule approximately 300 nucleotides in length. The M. voltae RNA molecule exhibits a strong similarity to both archaebacterial and eucaryotic 7S RNAs in terms of overall secondary structure, while the primary sequence is conserved to a lesser degree. All 7S RNA molecules possess a specific structural domain which is highly conserved in terms of both primary sequence and secondary structure, possibly representing a functional site of the molecule. Conservation of the 7S RNA molecule suggests that it is the descendant of a subcellular structure present before the divergence of the archaebacterial and eucaryotic kingdoms. The M. voltae 7S RNA gene is flanked both 5' and 3' by regions of extremely A + T-rich DNA. The 5'-flanking region contains several potential promoter sequences for archaebacterial RNA polymerases. One such sequence occurs as three direct repeats and bears a strong similarity to sequences found upstream of other archaebacterial genes. The 3'-flanking region contains a strong signal for the termination of transcription
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