Abstract
The expression of cystathionine γ-synthase (CGS), the key enzyme in methionine biosynthesis, is down-regulated in response to S-adenosylmethionine (SAM) at the level of mRNA stability. It has been suggested that this regulation occurs during translation. The first exon of CGS is necessary and sufficient for this regulation, and an amino acid sequence within exon 1 (the MTO1 region) is particularly important. Translation arrest has been observed when GST-tagged CGS exon 1 is translated in vitro. To determine the necessary region for translation arrest, 'stop codon-scanning' was performed. When the Lys-92 codon was replaced with UAG (K92stop) translation arrest product was not detected, whereas W93stop, S94stop, N95stop and N96stop produced growing amount of translation arrest products. Each codon of K92-N95 was substituted with Ala codon for further analysis. Translation arrest was not observed only when Trp93 was substituted with Ala, suggesting that Trp93 is critical for this regulation.
