Human transcription factors in yeast: the fruitful examples of P53 and NF-кB

The observation that human transcription factors (TFs) can function when expressed in yeast cells, has stimulated the development of various functional assays to investigate i) the role of binding site sequences (herein referred to as Response Elements, REs) in transactivation specificity, ii) the impact of polymorphic nucleotide variants on transactivation potential, iii) the functional consequences of mutations in TFs, and iv) the impact of cofactors or small molecules. These approaches have found applications in basic as well as applied research, including the identification and the characterization of mutant TF alleles from clinical samples. The ease of genome editing of yeast cells and the availability of regulated systems for ectopic protein expression enabled the development of quantitative reporter systems, integrated at a chosen chromosomal locus in isogenic yeast strains that differ only at the level of a specific RE targeted by a TF or for the expression of distinct TF alleles. In many cases, these assays were proven predictive of results in higher eukaryotes. The potential to work in small volume formats and the availability of yeast strains with modified chemical uptake have enhanced the scalability of these approaches. Next to well-established one-, two-, three- hybrid assays, the functional assays with non-chimeric human TFs enrich the palette of opportunities for functional characterization. We review about twenty-five years of research on human sequence-specific TFs expressed in yeast, with an emphasis on the P53 and NF-κB family of proteins, highlighting outcomes, advantages, challenges, and limitations of these heterologous assays.