Figure 1.

Roadmap highlighting the relationship between the SCF^Met30-Met4 interplay and the regulatory schemes involved in sulfur assimilation, oxidative stress and cell division. The model emphasizes the notion that the SCF^Met30 ubiquitin ligase activates the Met4 transcriptional activator in a manner linked to cell division and dependent on low levels of methionine, allowing expression of the MET and SAM genes encoding the enzymes assimilating sulfur into methionine and S-adenosyl-methionine, respectively (green). In a negative feedback response driven by methionine accumulation, with the biosynthesis of S-adenosyl-methionine and cysteine necessary in this regulatory context, Met4 activation by SCF^Met30 is blocked, leading to Met4 inhibition (purple). Navy blue indicates steps involved in oxidative stress response induced by cadmium (Cd²⁺). Note that Sam1 and Sam2 enzymes are necessary for all three types of responses, emphasizing the special regulatory role of S-adenosyl-methionine biosynthesis. Methionine, S-adenosyl-methionine and cysteine are necessary for the biosynthesis and modification of proteins, lipids and nucleotides during growth (turquoise). See text for details.