Dissecting the role of two activation domains in Zap1 in Saccharomyces cerevisiae

Zinc homeostasis in Saccharomyces cerevisiae is mediated by the transcriptional activator Zap1. Under zinc‐limiting conditions, Zap1 activates expression of over 40 genes involved in zinc acquisition and utilization. When zinc is abundant, Zap1 function is inactivated. Zap1 has two activation domains, AD1 and AD2, that increase gene transcription. Intriguingly, both of these domains are independently regulated by zinc. Furthermore, the presence of two activation domains is a feature evolutionarily conserved among Zap1 orthologs in other species suggesting the importance of both domains to cell physiology. In this study, we are assessing the contribution of AD1 and AD2 to Zap1 target gene regulation and zinc homeostasis. Using a Zap1 allele deleted for AD1, we demonstrated that AD2 varied greatly in its ability to drive transcription of different Zap1 target genes under low zinc conditions. While some genes were still highly expressed in cells expressing Zap1 lacking AD1, other genes were expressed at only low levels. Moreover, cells bearing the AD1 deletion allele showed a severe growth under zinc limiting conditions. These results demonstrate that AD1 is critical for normal growth under zinc limiting conditions and for the expression of many Zap1 target promoters. The contributions of AD2 to zinc homeostasis are currently being assessed using similar approaches.