A halt in poly(A) shortening during <i>S</i>-adenosyl-L-methionine-induced translation arrest in <i>CGS1</i> mRNA of <i>Arabidopsis thaliana</i>
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Cystathionine γ-synthase (CGS) catalyzes the first committed step of methionine (Met) biosynthesis in plants. Expression of the <i>Arabidopsis thaliana CGS1</i> gene is negatively feedback-regulated in response to the direct Met metabolite <i>S</i>-adenosyl-L-methionine (AdoMet). This regulation occurs at the step of mRNA stability during translation and is coupled with AdoMet-induced <i>CGS1</i>-specific translation arrest. In general, mRNA decay is initiated by a shortening of the poly(A) tail. However, this process has not been studied in detail in cases where regulatory events, such as programmed translation arrest, are involved. Here, we report that the poly(A) tail of the full-length <i>CGS1</i> mRNA showed an apparent increase from 50–80 nucleotides (nt) to 140–150 nt after the induction of <i>CGS1</i> mRNA degradation. This finding was unexpected because mRNAs that are destined for degradation harbored longer poly(A) tail than mRNAs that were not targeted for degradation. The results suggest that poly(A) shortening is inhibited or delayed during AdoMet-induced translation arrest of <i>CGS1</i> mRNA. We propose an explanation for this phenomenon that remains consistent with the recent model of actively translating mRNA. We also found that <i>CGS1</i> mRNA degradation intermediates, which are 5'-truncated forms of <i>CGS1</i> mRNA, had a short poly(A) tail of 10–30 nt. This suggests that poly(A) shortening occurs rapidly on the degradation intermediates. The present study highlights <i>CGS1</i> mRNA degradation as a useful system to understand the dynamic features of poly(A) shortening.
- Genes & Genetic Systems
Genes & Genetic Systems 88(4), 241-249, 2013
The Genetics Society of Japan