The functional exchangeability of pk- and k-turns in RNA structure.
Ribonuclease P RNA requires a sharply kinked RNA helix to make a loop-receptor interaction that creates the binding site for the substrate. In some forms of the ribozyme, this is accomplished by a k-turn, while others have a different element called the pk-turn. The structure of the pk-turn in RNase P of Thermotoga maritima is globally very similar to a k-turn, but lacks all the standard features of that structure, including long-range hydrogen bonds between the two helical arms. We show here that in an isolated RNA duplex, the pk-turn fails to adopt a tightly kinked structure, but rather is a flexible element. This suggests that the tertiary contacts of RNase P assist its folding into the required kinked structure. We find that we can replace the k-turn of the SAM-I riboswitch with the pk-turn, such that the resulting RNA retains its ability to bind SAM, although with lower affinity. We also find that we can replace the pk-turn of T. maritima RNase P with a standard k-turn (in either orientation) with retention of ribozyme activity. Thus, although the pk-turn cannot intrinsically fold into the kinked structure, it can be induced to fold correctly in context. And the pk-turn and k-turns can substitute functionally for one another.
Cancer Research UK Nucleic Acid Structure Research Group; MSI/WTB Complex; The University of Dundee; Dundee, UK.
Peter
P
Daldrop
Benoît
B
Masquida
David M J
DM
Lilley
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D031541:Fluorescence Resonance Energy Transfer; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D059372:Nucleotide Motifs; D059370:RNA Folding; D020871:RNA Stability; D012329:RNA, Bacterial / Q000737:chemistry*; D043262:Ribonuclease P / Q000737:chemistry* / Q000235:genetics; D058928:Riboswitch; D020124:Thermotoga maritima / Q000737:chemistry / Q000235:genetics*
D001426:Bacterial Proteins; D012329:RNA, Bacterial; D058928:Riboswitch; D043262:Ribonuclease P
RNA folding; RNA structure; RNase P; SAM-I riboswitch; kink turn