Met4 domain structure. TA: transactivating domain. IR: inhibitory region required for repression of Met4 activity by methionine. AUX: auxiliary domain required to fully relieve IR-mediated repression under activating conditions. INT: protein-protein interaction domain that binds Met31 and Met32. bZIP: basic leucine zipper domain that mediates Met4 dimerization and binding to Met28 as well as Cbf1. UIM: ubiquitin-interacting motif that prevents degradation of poly-ubiquitinated Met4. K163: ubiquitin acceptor site.