Decoding the genome: a modi®ed view Paul F. Agris - SURVEY AND SUMMARY

Oct 12, 2026

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Transfer RNA's role in decoding the genome is critical for accurate, efficient protein synthesis. Although modified nucleosides were identified decades ago, their importance in enabling tRNA recognition of cognate and wobble codons has become clear more recently. RNA modifications are widespread, with numerous posttranslational changes identified. tRNA modifications at the wobble and adjacent positions shape codon discrimination and wobble expansion, reducing anticodon loop dynamics to ribosome-accepted behavior, supporting selective decoding of amino-acid codons.

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Survey and summary

Abstract

Introduction

Genetic code background and anticodon-codon interaction

Published online January 9, 2004 Nucleic Acids Research, 2004, Vol. 32, No. 1 223±238 DOI: 10.1093/nar/gkh185 SURVEY AND SUMMARY Decoding the genome: a modi®ed view Paul F. Agris* Department of Molecular and Structural Biochemistry, 128 Polk Hall, Campus Box 7622, North Carolina State University, Raleigh, NC 27695-7622, USA Received November 13, 2003; Revised and Accepted December 2, 2003 ABSTRACT Transfer RNA's role in decoding the genome is critical to the accuracy and ef®ciency of protein synthesis. Though modi®ed nucleosides were identi®ed in RNA 50 years ago, only recently has their importance to tRNA's ability to decode cognate and wobble codons become apparent. RNA modi®cations are ubiquitous. To date, some 100 different posttranslational modi®cations have been identi-®ed. Modi®cations of tRNA are the most extensively investigated; however, many other RNAs have modi®ed nucleosides. The modi®cations that occur at the ®rst, or wobble position, of tRNA's anticodon and those 3¢-adjacent to the anticodon are of particular interest. The tRNAs most affected by individual and combinations of modi®cations respond to codons in mixed codon boxes where distinction of the third codon base is important for discriminating between the correct cognate or wobble codonsand the incorrect near-cognate codons (e.g. AAA/G for lysine versus AAU/C asparagine). In contrast, other modi®cations expand wobble codon recognition, such as U´U base pairing, for tRNAs that respond to multiple codons of a 4-fold degenerate codon box (e.g. GUU/A/C/G for valine). Whether restricting codon recognition, expanding wobble, enabling translocation, or maintaining the messenger RNA, reading frame modi®cations appear to reduce anticodon loop dynamics to that accepted by the ribosome. Therefore, we suggest that anticodon stem and loop domain nucleoside modi®cations allow a limited number of tRNAs to accurately and ef®ciently decode the 61 amino acid codons by selectively restricting some anticodon±codon interactions and expanding others. INTRODUCTION Very often, our understanding of biology is derived from atestable hypothesis and the experimental results that follow. So it was in understanding how genetic information encoded in DNA was transformed by the cell into a unique sequence of a protein's amino acids. With the ®rst mention of the adaptor molecule hypothesis came a search for and the testing ofsRNA's (tRNA's) ability to translate genetic information (1) . A set of coding triplets or three letter codes composed of thenucleosides adenosine (A), guanosine (G), cytidine (C) and uridine (U) was envisioned to account for the 20 amino acids (2) . The three letter code was supported by experiments in vivo including some of the earliest applications of translational frameshifting (3) . In vitro, speci®c coding triplets were associated with individual amino acids through ribosomemediated aminoacyl-tRNA binding to either homopolymers, enzymatically synthesized heterotriplets (4,5) or chemically synthesized polynucleotides (6±9) . The deciphering of the triplets resulted in what is now the historical presentation of the Genetic Code (Fig. 1) . The ®rst two letters of the code, A, G, C or U, create 16 possible combinations, each of which is displayed in a separate `codon box'. Each codon box is composed of four, three letter codes, 64 in all. Sixty-one codons are recognized by tRNAs for the incorporation of amino acids, and three codons signal the termination of protein synthesis. Eight of the codon boxes each code for only a single amino acid and therefore, are 4-fold degenerate (Fig. 1) . The remaining 12 amino acids have codons in 2-fold degenerate codon boxes (e.g. asparagine and lysine, or tyrosine and stop), are 3-fold degenerate (isoleucine), or have only one codon (e.g. methionine and tryptophan) . The evident degeneracy of the genetic code required that amino acid speci®c tRNAs respond to multiple coding triplets that differed only in the

FAQs

Why is tRNA modification important for decoding the genome?

tRNA modifications affect the accuracy and efficiency of protein synthesis by shaping how anticodons interact with cognate and wobble codons.

Which tRNA positions are highlighted as most important for codon recognition?

Modifications at the first (wobble) position of the anticodon and those 3¢-adjacent to the anticodon are emphasized as especially influential.

How do different tRNA modifications affect wobble codon recognition?

Some modifications restrict codon recognition, while others expand wobble recognition (for example through U´U base pairing), allowing responses to multiple codons in degenerate codon boxes.

Oct 12, 2026

Uploaded by dabgoudw