Journal of Biological Chemistry
Volume 277, Issue 33, 16 August 2002, Pages 29654-29661
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RNA: STRUCTURE METABOLISM AND CATALYSIS
The Physiological Role of RNase T Can Be Explained by Its Unusual Substrate Specificity*

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Escherichia coli RNase T, the enzyme responsible for the end-turnover of tRNA and for the 3′ maturation of 5 S and 23 S rRNAs and many other small, stable RNAs, was examined in detail with respect to its substrate specificity. The enzyme was found to be a single-strand-specific exoribonuclease that acts in the 3′ to 5′ direction in a non-processive manner. However, although otherEscherichia coli exoribonucleases stop several nucleotides downstream of an RNA duplex, RNase T can digest RNA up to the first base pair. The presence of a free 3′-hydroxyl group is required for the enzyme to initiate digestion. Studies with RNA homopolymers and a variety of oligoribonucleotides revealed that RNase T displays an unusual base specificity, discriminating against pyrimidine and, particularly, C residues. Although RNase T appears to bind up to 10 nucleotides in its active site, its specificity is defined largely by the last 4 residues. A single 3′-terminal C residue can reduce RNase T action by >100-fold, and 2-terminal C residues essentially stop the enzyme. In vivo, the substrates of RNase T are similar in that they all contain a double-stranded stem followed by a single-stranded 3′ overhang; yet, the action of RNase T on these substrates differs. The substrate specificity described here helps to explain why the different substrates yield different products, and why certain RNA molecules are not substrates at all.

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Published, JBC Papers in Press, June 5, 2002, DOI 10.1074/jbc.M204252200

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This work was supported by Grant GM16317 from The National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.