Molecular Mechanism of Nascent Peptide-Mediated Translation Arrest Involved in Feedback Regulation of Methionine Biosynthesis

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Cystathionine γ-synthase (CGS) catalyzes the first committed step of methionine biosynthesis in plants, and is encoded by CGS1 gene in Arabidopsis. Expression of CGS1 is feedback-regulated at the step of CGS1 mRNA degradation and S-adenosyl-L-methionine (SAM) acts as an effector. We found that, when ribosome translates the CGS1 mRNA in the presence of SAM, either the ribosome itself or the nascent peptide within the ribosomal exit tunnel changes its conformation. We also obtained evidence suggesting that the ribosomal proteins that constitute the exit tunnel is involved in this regulation.