Translation Elongation Arrest and Coupled mRNA Decay Mechanisms for Regulation of the Arabidopsis CGS1 Gene that Encodes a Key Enzyme in Methionine Biosynthesis

Abstract

Expression of the Arabidopsis CGS1 gene that encodes cystathionine γ-synthase, which catalyzes the first committed step of methionine biosynthesis, is feedback-regulated at the step of mRNA stability in response to S-adenosylmethionine (SAM). A short stretch of amino acid sequence, termed the MTO1 region, encoded by the first exon of CGS1 itself is involved in this regulation by acting in cis. In vitro studies using wheat germ extract revealed that translation of CGS1 mRNA is temporally arrested in response to SAM prior to mRNA degradation. This translational pausing occurs immediately after translating the MTO1 region. Based on these observations, we propose a model in which nascent MTO1 peptide acts in the ribosome that has just translated the MTO1 region to cause translational pausing in response to SAM, and the translation elongation arrest triggers mRNA degradation.