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

半胱硫氨酸γ合成酶催化植物甲硫氨酸生物合成的第一步，在拟南芥中由CGS1基因编码。在CGS1mRNA降解过程中，CGS1mRNA的表达受到反馈调控，S-腺苷-L-蛋氨酸作为效应因子。我们发现，当核糖体在SAM存在的情况下翻译CGS1 mRNA时，核糖体本身或核糖体出口通道内的新生多肽改变了其构象。我们还获得了证据表明，构成出口通道的核糖体蛋白参与了这一调控。

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.