Nucleic Acids Research, 1992, Vol. 20, No. 11 2835-2840
© 1992
MOLECULAR BIOLOGY |
Extensive phosphorothioate substitution yields highly active and nuclease-resistant hairpin ribozymes
Department of Microbiology and Molecular Genetics, Markey Center for Molecular Genetics, The University of Vermont Burlington, VT 05405, USA
*To whom correspondence should be addressed
Received January 24, 1992. Revised April 29, 1992. Accepted April 29, 1992.
The catalytic function of the hairpin ribozyme has been investigated by modification-interference analysis of both ribozyme and substrate, using ribonucleoside phosphorothioates. Thiophosphate substitutions in two ribozyme domains were examined by using a novel and highly efficient two-piece ribozyme assembled from two Independently synthesized oligoribonucleotides. The catalytic proficiency of the two-piece construct (KM= 48nM, kcat= 2.3 min1) is nearly identical to that of the one-piece ribozyme. The two-piece ribozyme is essentially unaffected by substitution with thiophosphates 5' to all guanosines, cytidines, and uridines. In contrast, incorporation of multiple adenosine phosphorothioates in the 5' domain of the ribozyme decreases ribozyme activity by a factor of 25. Modification-interference experiments using ribozymes partially substituted with adenosine phosphorothioate suggest that thiophosphates 5' to A7, A9 and A10 interfere with cleavage to a greater extent than substitutions at other sites within the molecule, but the effect is modest. Within the substrate, phosphorothioate substitution does not directly interfere with cleavage, rather, increasing thiophosphate content decreases the stability of the rlbozyme-substrate complex. We describe the construction of a hairpin ribozyme containing dinucleotide extensions at its 5' and 3' ends. Full substitution of this molecule with G and C phosphorothioates results in a ribozyme with greatly enhanced stability against cellular ribonucleases without significant loss of catalytic efficiency.
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