Abstract
Expression of the Arabidopsis CGS1 gene that codes for cystathionine γ-synthase (CGS) is feedback-regulated at the step of mRNA stability 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 intermediates of mRNA degradation accumulate that are truncated at their 5' region. Primer extension experiments revealed several different 5' ends of the intermediate that are separated by approximately 30 nucleotides from each other. In addition, multiple translation products that likely corresponded to jammed ribosomes were also detected. These results demonstrate that SAM induces ribosome stacking on the CGS1 mRNA, which likely determines the mRNA degradation points.
