Transcriptional re-wiring by mutation of the yeast Hsf1 oligomerization domain

Response to heat stress is mediated by heat shock transcription factors (HSFs), which possess conserved DNA-binding and oligomerization domains. The oligomerization domain is required for HSF1 to transition under heat stress from a monomer to a homotrimer, which alters DNA-binding specificity and affinity. Sequence variation in the oligomerization domain affects HSF1 activity, although this link is poorly understood. We performed a deep mutational scan of >400,000 variants of the oligomerization domain of Saccharomyces cerevisiae Hsf1 and measured fitness under stress and non-stress conditions. We identify mutations that confer temperature-specific phenotypes; some exceptional Hsf1variants lead to enhanced growth under heat stress and changes to in vivo DNA-binding and transcriptional programs. The link between Hsf1 oligomerization and DNA-binding domain is evolutionarily conserved, with co-evolving residues between these domains found among fungi. Mutation of transcription factor oligomerization domains may represent a path toward re-wiring transcriptional programs without mutation of DNA-binding domains.