The effect of reducing reagents on binding of thymidylate synthase protein to thymidylate synthase messenger RNA

Human thymidylate synthase (TS) protein specifically binds to its own TS mRNA and functions as a translational repressor. In the presence of reducing agents, the RNA binding activity of TS protein is significantly enhanced. In contrast, treatment of TS protein with the oxidizing agent diamide inhibits RNA binding. Scatchard analysis reveals that in the presence of the reducing agent 2-mercaptoethanol, the TS protein/TS mRNA interaction changes from low (K(d) = 66 nM) to high (K(d) = 2.6 nM) apparent affinity. The catalytic activity of TS is increased by up to 6.5-fold in the presence of 2- mercaptoethanol. These studies demonstrate that the interaction between TS protein and its target TS mRNA is sensitive to the presence of reducing reagents and is dependent upon a reversible sulfhydryl switch mechanism.