A re-investigation of the thio effect at the hammerhead cleavage site.
The effect of introducing a phosphorothioate at the hammerhead cleavage site was investigated using a kinetically well-characterized hammerhead. In buffers containing Mg ion, the RP-phosphorothioate isomer cleaved 2000- to 80 000-fold slower than the SPisomer or the unmodified RNA substrate. Addition of low concentrations of several thiophilic metal ions, especially Cd2+, to these reactions is sufficient to fully restore the cleavage rate of the RPsubstrate without affecting cleavage rate of the all-oxygen or SPsubstrate. Thus, a model proposing coordination of a divalent metal ion to the pro-R oxygen at the hammerhead cleavage site appears justified.
Scott
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Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA.
Uhlenbeck
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D002021:Buffers; D002104:Cadmium; D002384:Catalysis; D002413:Cations, Divalent; D007536:Isomerism; D007700:Kinetics; D009690:Nucleic Acid Conformation; D012323:RNA Processing, Post-Transcriptional; D016337:RNA, Catalytic / Q000737:chemistry / Q000378:metabolism*; D013873:Thionucleotides / Q000378:metabolism*
D002021:Buffers; D002413:Cations, Divalent; D016337:RNA, Catalytic; D013873:Thionucleotides; D002104:Cadmium