Architecture of ribosomal RNA: constraints on the sequence of "tetra-loops".
The four-base loops that cap many double-helical structures in rRNA (the so-called "tetra-loops") exhibit highly invariant to highly variable sequences depending upon their location in the molecule. However, in the vast majority of these cases the sequence of a tetra-loop is independent of its location and conforms to one of three general motifs, GNRA, UNCG, and (more rarely) CUUG. For the most frequently varying of the 16S rRNA tetra-loops, that at position 83 (Escherichia coli numbering), the three sequences CUUG, UUCG, and GCAA account for almost all examples encountered, and each of them has independently arisen at least a dozen times. The closing base pair of tetra-loop hairpins reflects the loop sequence, tending to be C.G for UUCG loops and G.C for CUUG loops.
Woese
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CR
Department of Microbiology, University of Illinois, Urbana 61801.
Winker
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Gutell
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RR
D001419:Bacteria / Q000235:genetics; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012336:RNA, Ribosomal, 16S / Q000737:chemistry*; D013045:Species Specificity
D012336:RNA, Ribosomal, 16S