Abstract
Cystathionine γ-synthase (CGS), which catalyzes the key step of methionine biosynthesis, is encoded by CGS1 gene in Arabidopsis. Expression of CGS1 is feedback-regulated at the step of mRNA degradation in response to S-adenosyl-L-methionine (AdoMet). A 14-amino-acid sequence, termed the MTO1 sequence, located near the N-terminal region of CGS itself is important for this regulation by acting in cis. This CGS1 mRNA degradation is preceded by temporal translation arrest that occurs at Ser-94 located immediately downstream of the MTO1 sequence. This implies that the MTO1 peptide exists in the exit tunnel of the arrested ribosome.
In an attempt to gain insights into the molecular function of MTO1 sequence in the exit tunnel, we explored the possibility that AdoMet induces a structural alteration of the CGS1 nascent peptide covering the MTO1 sequence. We examined this possibility by pegylation assay using an in vitro translation system. The results indicated that AdoMet induces a compact structure formation in CGS1 nascent peptide in an MTO1 sequence-dependent manner. Correlation between nascent peptide compaction and translation arrest will be discussed.
