Zinc-Finger 5 Is an Activation Domain in the Saccharomyces cerevisiae Stress-Responsive Transcription Factor Fzf1

Fzf1 is a Saccharomyces cerevisiae transcription factor that contains five zinc finger domains (ZF1-5) and induces the expression of at least five genes in response to various chemical stresses by recognizing the shared promoter consensus sequence CS2. The N-terminal ZF1-3 are required and sufficient for binding to CS2, while ZF4 negatively regulates the activity of Fzf1. However, the effect of ZF5 on the activity of Fzf1 is not well defined. In this study, substitutions of the two zinc-coordinating Cys residues (C248S and C253S) of ZF5, or deletion of the whole ZF5 domain, compromised the chemical stress-induced activation of Fzf1. Since the elevated Fzf1-regulated gene expression caused by fzf1-ZF4 could also be reversed by additional deletion of ZF5 or C248S/C253S substitutions, fzf1-ZF5 mutations are epistatic over fzf1-ZF4 mutations. Furthermore, fzf1-ZF5 mutations are recessive to FZF1, while ZF5 is dispensable for the CS2 binding. Finally, Fzf1-ZF5 is required and sufficient to serve as a transcription activation domain when fused to a Gal4 DNA-binding domain. These observations collectively support a working model in which Fzf1 bound to its target gene promoters remains inactive due to an inhibitory activity of ZF4. Upon chemical stress, ZF4 is no longer able to inhibit the ZF5 transactivation activity, leading to the induction of Fzf1-regulated gene expression and subsequent chemical detoxification.