Abstract
Expression of Arabidopsis cystathionine γ-synthase (CGS), the key step in methionine biosynthesis, is feedback regulated at the step of mRNA degradation in response to <S>-adenosyl-L-methiomine (SAM). The first exon coding region of CGS is necessary and sufficient for this regulation. A short stretch of amino acid sequence (MTO1 region) is particularly important for this regulation. A nascent peptide emerges after passing through the exit tunnel of ribosome. We suggest a model that the nascent peptide and SAM interact inside the exit tunnel. We introduced amino acid substitutions at Cys-80 and Ser-81, and analyzed their response to SAM and <S>-adenosyl-L-ethionine (SAE) which has ethyl group in place of methyl, and found differences in their response. Here, we suggest that Cys-80 and Ser-81 play a role in recognition of methionine and ethionine.
