The hammerhead cleavage reaction in monovalent cations.
Recently, Murray et al. (Chem Biol, 1998, 5:587-595) found that the hammerhead ribozyme does not require divalent metal ions for activity if incubated in high (> or =1 M) concentrations of monovalent ions. We further characterized the hammerhead cleavage reaction in the absence of divalent metal. The hammerhead is active in a wide range of monovalent ions, and the rate enhancement in 4 M Li+ is only 20-fold less than that in 10 mM Mg2+. Among the Group I monovalent metals, rate correlates in a log-linear manner with ionic radius. The pH dependence of the reaction is similar in 10 mM Mg2+, 4 M Li+, and 4 M Na+. The exchange-inert metal complex Co(NH3)3+ also supports substantial hammerhead activity. These results suggest that a metal ion does not act as a base in the reaction, and that the effects of different metal ions on hammerhead cleavage rates primarily reflect structural contributions to catalysis.
Curtis
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Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Cambridge 02142, USA.
Bartel
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D001483:Base Sequence; D002414:Cations, Monovalent / Q000737:chemistry / Q000494:pharmacology*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016337:RNA, Catalytic / Q000187:drug effects / Q000378:metabolism*; D014508:Urea / Q000494:pharmacology
D002414:Cations, Monovalent; D016337:RNA, Catalytic; D014508:Urea