Abstract
Cystathionine γ-synthase (CGS) catalyzes the key step of methionine biosynthesis. Expression of AtCGS1 is down-regulated at the step of mRNA stability in response to S-adenosylmethionine (SAM). A short amino acid sequence within the first exon coding region of AtCGS1 is important. Translation arrest is observed prior to mRNA degradation in the cell-free translation system of wheat germ extract, and Trp-93 located right before the arrest site is important. Although Trp-93 is conserved among angiosperms, the two CGS sequences of Physcomitrella patens have Ala. In vitro translation of PpCGS sequences corresponding to the AtCGS1 exon 1 was performed. The PpCGS sequences responded to SAM, although the response was weaker than in AtCGS1. When the Ala codon was substituted with Trp, accumulation of mRNA degradation intermediate and translation arrest product was promoted. These results suggest that Trp-93 promotes the translation arrest, and that additional elements are required for the efficient arrest.
