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RNA minihelices as model substrates for ATP/CTP:tRNA nucleotidyltransferase
Z Li1, Y Sun, D L Thurlow
1Department of Chemistry, Clark University, 950 Main Street, Worcester, MA 01610, USA.
The Biochemical Journal
|May 15, 1998
Summary
RNA minihelices were tested as substrates for tRNA nucleotidyltransferases. Loop base identity influenced substrate efficiency, with purines generally performing better than pyrimidines.
Area of Science:
- Molecular Biology
- Biochemistry
- RNA Structure
Background:
- Transfer RNA (tRNA) nucleotidyltransferases play a crucial role in tRNA metabolism.
- The acceptor/T-stems and T-loop of tRNA are critical for its three-dimensional structure and function.
- Understanding substrate specificity of these enzymes is key to elucidating tRNA processing pathways.
Purpose of the Study:
- To investigate the substrate capabilities of synthetic RNA minihelices for tRNA nucleotidyltransferases.
- To determine how variations in the T-loop sequence of minihelices affect enzyme interaction.
- To compare the enzymatic activity of Escherichia coli and Saccharomyces cerevisiae tRNA nucleotidyltransferases on these minihelical substrates.
Main Methods:
- Synthesis of 21 RNA minihelices with varied T-loop sequences.
- Enzymatic assays using ATP/CTP:tRNA nucleotidyltransferases from E. coli and S. cerevisiae.
- Kinetic analysis (Km and Vmax) of minihelix substrates compared to natural tRNA.
Main Results:
- All synthesized RNA minihelices served as substrates for both enzymes.
- The identity of bases within the minihelix T-loop significantly impacted substrate efficiency.
- Purine-containing loops generally showed higher substrate activity than pyrimidine-containing loops.
- Minihelices lacking 5'-terminal bases were better substrates for E. coli enzyme than yeast enzyme.
- Apparent Km values for minihelices were 2-3 times higher, and apparent Vmax values were 5-10 times lower than for natural tRNA.
Conclusions:
- RNA minihelices are viable substrates for tRNA nucleotidyltransferases, providing insights into enzyme-substrate interactions.
- T-loop sequence composition is a critical determinant of substrate recognition and processing efficiency.
- Enzyme variants from different species (E. coli vs. S. cerevisiae) exhibit distinct substrate preferences, particularly concerning RNA structural elements near the 5'-end.