Positive trans-acting factor capable of stimulating the transcription of the MET genes from the methionine biosynthetic pathway. MET4, MET28 and CBF1 are required for full induction of MET25 and MET16 gene transcription. MET4 controls as well the derepression of MET6. Required for the transcription of genes necessary for sulfur amino acid biosynthesis. Involved in the transcription activation of MET28 and MET30. Required for MET3 gene expression via assembly of the MET4-MET28-MET31 and MET4-MET28-MET32 complexes. Involved in response to cadmium and arsenic. Cadmium-activated MET4 also induces glutathione biosynthesis. Interacts with MET30. Tethered to DNA through two alternate complexes associating MET4 with MET28 and either MET31 or MET32. Interacts with MET28 and CBF1 through its leucine zipper to form a heteromeric complex. Regulated by the general amino acid control. The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. Present with 1300 molecules/cell in log phase SD medium. Transcriptional activation function is inhibited by the elevation of intracellular S-adenosylmethionine (AdoMet), but is activated by cadmium and arsenic which leads to phosphorylation and prevents ubiquitination. Inactivation by oxidative stress induced by hydrogen peroxide promotes ubiquitination. Belongs to the bZIP family.