Figure 14.

Models for Met4 recruitment to MET (A) versus PDC6 (B) promoters. Met4 recruitment involves direct interactions with Cbf1 (through the bZIP domain) and Met31 or Met32 (through the ‘Int’ domain). Met28 associates with Met4 bZIP and participates in Met4 recruitment through stabilization of the Met4–Cbf1–DNA complex (see text for details and references). The question marks at the extremity of the arrows originating from Met4 bZIP indicate that, even though direct interactions with promoter DNA are likely [see ref. (16)], the precise points of contact remain to be established. At PDC6 promoter, Met31 and Met32 bind to two distinct sites. Met4 recruitment to this promoter requires interaction with Met32 specifically, and Met31 participates by assisting Met32 association with its binding site. The width of the arrows pointing toward Cbf1 and Met31/32 DNA binding sites translate the strength of the interaction, which differs between MET and PDC6 promoters.