Figure 10.

Model for the regulation of Asf1/HIR complex heterochromatin function. In the absence of DNA damage, Mec1 and Dun1 have opposing roles in balancing the cellular concentration of active Asf1. Mec1 promotes the dissociation of the Rad53-Asf1 complex, whereas Dun1 blocks ectopic activation of Rad53. In the proposed model, Hir protein association with Asf1 requires dissociation of the Rad53-Asf1 complex. As a result, Mec1 and Dun1 would influence the levels of Asf1-Hir complex formation that is critical for heterochromatin-mediated gene silencing.