Acts as an accessory factor in the activation of sulfur amino acids metabolism genes. Possesses no intrinsic transcription activation abilities. Binds to the MET16 promoter as a complex with MET4 and CBF1. Enhances the DNA-binding activity of CBF1. Interacts with MET4 to form a heteromeric complex which also includes CBF1. Forms two alternate complexes associating MET28 with MET4 and either MET31 or MET32. Binds to DNA through the MET4-MET28-CBF1 complex. Expression requires MET4, and is repressed by an increase of intracellular S-adenosylmethionine (AdoMet). Belongs to the bZIP family.