Abstract
Cystathionine γ-synthase (CGS) catalyzes the first committed step of methionine biosynthesis. Expression of the CGS gene is feedback-regulated at the level of mRNA stability by S-adenosylmethionine (SAM) in Arabidopsis. There is a 41 amino acid region of exon 1 that is highly conserved among plant species (conserved region). Since the exon 1 polypeptide acts in cis, we have proposed that the regulation occurs during translation. We used a wheat germ extract translation system to analyze the decay intermediate of CGS mRNA. When in vitro-transcribed RNA carrying CGS exon 1 was translated in the presence of SAM, a 5'-truncated RNA that was about 300 bases shorter than the full-length RNA was detected. Analyses of a series of deletions within CGS exon 1 revealed that the conserved region is necessary and sufficient for production of the 5'-truncated RNA.
