Multiple domains mediate heme control of the yeast activator HAP1.

The activity of the yeast activator HAP1 in vivo requires heme. A heme responsive domain of HAP1 was identified previously. It is adjacent to the DNA-binding domain and appears to block DNA binding in the absence of heme. Here we describe a novel genetic selection which yielded mutants of HAP1 that are independent of heme when assayed for activation. These mutants define a second region of HAP1, close to the activation domain, which also controls its response to heme.