FIG. 7.

Model illustrating the action of HRMs and Hsp90 in heme activation of Hap1. Hsp90 associates with Hap1 in the absence of heme. Based on previous studies (24) and data presented in this report, we postulate that the interaction of Hsp90 with Hap1 causes Hap1 to adopt a conformation that can readily bind to heme and is activable. Upon heme binding, Hsp90 acts with Hap1 to initiate further conformational or structural changes, thereby leading to full Hap1 activation. Mutations in Hap1 may cause Hap1 to lose its ability to adopt an activable conformation so that it cannot bind to heme or cannot induce further conformational changes necessary for activation following heme binding. For simplicity, other proteins, including Ssa, Ydj1, and Sro9, are omitted from this diagram.