Abstract
Expression of the Arabidopsis CGS1 gene that encodes cystathionine γ-synthase (CGS) is feedback-regulated at the step of mRNA degradation in response to S-adenosyl-L-methionine (SAM). The CGS1 regulation is reproduced in a cell-free system, and we found that SAM induces translational pausing prior to mRNA degradation. These events produce partial translation products and several different mRNA degradation intermediates. Analyses of these products revealed that SAM induces ribosome stacking. Furthermore, the translation arrest product, peptidyl-tRNA, resides at the A site of the primarily arrested ribosome.
To analyze the state of the A site of stalled ribosomes, we used puromycin, a translation elongation inhibitor. The primarily arrested ribosome showed a low sensitivity to puromycin, while the other stacked ribosomes showed a normal one. These results suggest that the state of the A site of the primarily arrested ribosome is different from those of the others.
