Abstract
Expression of the Arabidopsis CGS1 gene that codes for cystathionine γ-synthase (CGS) is feedback-regulated at the step of mRNA degradation in response to S -adenosyl-L-methionine (SAM). This regulation occurs during translation and a short stretch of amino acid sequence (MTO1 region) encoded by the first exon of CGS1 itself is involved in this regulation. Recently, we found that SAM induces translational pausing prior to the mRNA degradation.
CGS1 regulation is reproduced in a cell-free system, and several different intermediates of mRNA degradation accumulate that are truncated at their 5' region. A line of evidence suggests that SAM induces ribosome stacking and the multiple mRNA degradation points correspond to each of the stacked ribosomes. When we analyzed degradation intermediates of mRNAs containing phosphorothioate linkages, which are thought to be resistant to nucleases, intermediates identical to those of unmodified mRNA were detected. This suggests that endonucleolytic cleavages are involved in CGS1 mRNA degradation.