- Precise recognition of tRNAs by their cognate aminoacyl-tRNAsynthetases is crucial for the fidelity of protein synthesis. In the context of the aminoacylationof tRNAAlawith its cognate aminoacyl-tRNAsynthetase(AlaRS) and based on the studies on the molecules Escherichia coli origin, following statements are made. Which one of the statements is INCORRECT?
(1) Anticodon of tRNAAlamakes important contribution to the specificity of its aminoacylation by AlaRSAlaRS
(2) Mutational analyses have shown that for of aminoacylation of the tRNAAla by AlaRS, the presence of a wobble pair in the acceptor stem (G3:U70) is the most crucial element.
(3) Aminoacylation of tRNAAla by AlaRS occurs even if the anticodon of tRNAAla is mutated.
(4) A microhelix lacking a clover leafstructure and harboring only the acceptor stem sequence of the tRNAAla is specifically aminoacylated by AlaRS.Specificity of Alanyl-tRNA Synthetase (AlaRS) in Aminoacylation of tRNA^Ala: Insights from Escherichia coli
Alanyl-tRNA synthetase (AlaRS) is responsible for charging tRNA^Ala with alanine, a critical step ensuring fidelity in protein synthesis. Studies on Escherichia coli AlaRS have revealed key features about how this enzyme recognizes its cognate tRNA and catalyzes aminoacylation.
Evaluating the Statements about AlaRS and tRNA^Ala Aminoacylation
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Anticodon of tRNA^Ala makes important contribution to specificity of aminoacylation by AlaRS
This statement is incorrect. Unlike many other aaRSs, AlaRS recognition of tRNA^Ala is largely independent of the anticodon. Instead, the major identity determinant lies elsewhere. -
Mutational analyses show that the presence of a wobble base pair G3:U70 in the acceptor stem is the most crucial element for aminoacylation of tRNA^Ala by AlaRS
This is correct. The G3:U70 wobble base pair in the acceptor stem is the primary identity element recognized by AlaRS, crucial for specific aminoacylation. -
Aminoacylation of tRNA^Ala by AlaRS occurs even if the anticodon of tRNA^Ala is mutated
This is correct. Mutations in the anticodon do not significantly affect aminoacylation efficiency, underscoring the minor role of the anticodon in AlaRS specificity. -
A microhelix lacking the cloverleaf structure but harboring only the acceptor stem sequence of tRNA^Ala is specifically aminoacylated by AlaRS
This is correct. The acceptor stem alone, especially the G3:U70 base pair, is sufficient for recognition and aminoacylation by AlaRS.
Explanation
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The G3:U70 wobble base pair in the acceptor stem is a unique and conserved identity element for tRNA^Ala across species.
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AlaRS interacts primarily with this base pair and the acceptor stem, rather than the anticodon loop, which is unusual among aminoacyl-tRNA synthetases.
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Experimental evidence shows that even minimal tRNA structures (“microhelices”) containing the acceptor stem and G3:U70 are recognized and aminoacylated by AlaRS.
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This highlights the evolutionary specialization of AlaRS for high-fidelity recognition through a simple but highly specific structural element.
Summary Table
Statement Correctness (1) Anticodon contributes importantly to specificity Incorrect (2) G3:U70 wobble pair in acceptor stem is most crucial identity element Correct (3) Aminoacylation occurs even if anticodon mutated Correct (4) Microhelix with acceptor stem alone is aminoacylated specifically Correct
Keywords for SEO Optimization
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Alanyl-tRNA synthetase specificity
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tRNA^Ala G3:U70 wobble base pair
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Aminoacylation of tRNA acceptor stem
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Protein synthesis fidelity
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AlaRS recognition mechanism
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Minimal tRNA structures in aminoacylation
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Escherichia coli AlaRS studies
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tRNA identity elements
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Aminoacyl-tRNA synthetase and anticodon independence
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Molecular basis of tRNA charging
Conclusion
The incorrect statement among the options is that the anticodon of tRNA^Ala makes an important contribution to specificity in aminoacylation by AlaRS. In reality, the G3:U70 wobble base pair in the acceptor stem is the critical identity element, and aminoacylation proceeds efficiently even if the anticodon is mutated. Moreover, a minimal tRNA structure containing only the acceptor stem can be specifically aminoacylated by AlaRS.
Correct answer: (1) Anticodon of tRNA^Ala makes important contribution to the specificity of its aminoacylation by AlaRS (This statement is incorrect).
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