Acetate-dependent tRNA acetylation required for decoding fidelity in protein synthesis

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Accurate protein translation relies on tRNA anticodon modifications.
• N4-acetylcytidine (ac4C) at position 34 of bacterial tRNA(Met) is essential for translation fidelity.
• The specific enzyme responsible for ac4C34 formation remained unidentified in Bacillus subtilis.

Purpose of the Study:

• To identify the gene responsible for ac4C34 formation in Bacillus subtilis.
• To elucidate the mechanism of ac4C34 synthesis.
• To investigate the functional relationship between ac4C34 and lysidine (L34) modifications in preventing codon misreading.

Main Methods:

• Gene identification and knockout (ΔtmcAL strain creation).
• Biochemical assays to study TmcAL activity and mechanism.
• X-ray crystallography to determine TmcAL structure.
• Genetic interaction studies with the tilS gene.

Main Results:

• Bacillus subtilis ylbM (renamed tmcAL) was identified as the novel gene for ac4C34 formation.
• TmcAL utilizes a unique mechanism, activating acetate to form acetyladenylate, distinct from typical acetyltransferases.
• Crystal structure of TmcAL revealed the molecular basis of ac4C34 synthesis.
• The ΔtmcAL strain exhibited cold sensitivity and interacted genetically with tilS.
• Repression of tilS in the ΔtmcAL strain led to mistranslation of the AUA codon as Met.

Conclusions:

• TmcAL is a novel enzyme catalyzing ac4C34 formation via an aminoacylation-like mechanism.
• ac4C34 modification of tRNA(Met) and L34 modification of tRNA(Ile) cooperatively prevent AUA codon misdecoding.
• These tRNA modifications are critical for maintaining translational accuracy, particularly under stress conditions like cold sensitivity.