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 t o the DNA-binding domain, and appears to block DNA binding in the abse nce of heme. Here we describe a novel genetic selection which yielded mutants of HAP1 that are independent of heme when assayed for activati on. These mutants define a second region of HAP1, close to the activat ion domain, which also controls its response to heme.