Abstract
Accumulation of Arabidopsis cystathionine γ-synthase (CGS) mRNA is down-regulated in response to S -adenosyl-L-methionine (SAM). A nascent polypeptide encoded by the CGS itself is important in this regulation. Recently, we found that SAM induces translational pausing prior to the mRNA degradation in a cell-free system.
We used this cell-free system to study the CGS mRNA degradation mechanism. Upon degradation, 5'-truncated mRNA species are produced as degradation intermediate. Primer extension experiments revealed several different 5' ends of the intermediate that are separated by approximately 30 nucleotides from each other. Since a ribosome covers about 30 nucleotides of the mRNA, we hypothesized that ribosomes stacked on the CGS mRNA determines the 5' end points. In a sucrose density gradient centrifugation experiment, number of the 5' ends increased as the faster-sedimenting fractions were used, which supports our hypothesis.
