The sequence of the 16S RNA gene from the archaebacterium Desulfurococcus mobilis and its flanking regions were determined. The mature RNA transcript is 1,495 nucleotides long. The putative secondary structure exhibits typical archaebacterial features and is closely related to those of the other extreme thermophile RNAs. This structure exhibits a very high level of G-C base pairing (74%) and it is possible for this and other thermophile structures to extend the regular base pairing into the internal loops which may reflect adaptation to high temperature. The 16S RNA structure is enclosed by a long processing stem containing a few irregularities that is characteristic of prokaryotes. The structure of 16S RNA from D. mobilis was aligned with all of the sequenced archaebacterial 16S RNAs and E. coli 16S RNA, and homology values were determined. A phylogenetic tree was derived from these values which showed that D. mobilis, Sulfolobus solfataricus and Thermoproteus tenax constitute a separate phylogenetic group. Of these D. mobilis exhibits the lowest genetic drift while T. tenax shows the deepest branching. © 1987, Gustav Fischer Verlag, Stuttgart · New York. All rights reserved.
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