6533b826fe1ef96bd1283d7a

RESEARCH PRODUCT

Engineering the smallest transcription factor: accelerated evolution of a 63-amino acid peptide dual activator-repressor

subject

description

Transcription factors control gene expression in all life. This raises the question of what is the smallest protein that can support such activity. In nature, Cro from bacteriophage λ is the smallest known repressor (66 amino acids; a.a.) but activators are typically much larger (e.g. λ cI, 237 a.a.). Indeed, previous efforts to engineer a minimal activator from Cro resulted in no activityin vivo. In this study, we show that directed evolution results in a new Cro activator-repressor that functions as efficiently as λ cI,in vivo. To achieve this, we develop Phagemid-Assisted Continuous Evolution: PACEmid. We find that a peptide as small as 63-a.a. functions efficiently as an activator and/or repressor. To our knowledge, this is the smallest protein gene regulator reported to date, highlighting the capacity of transcription factors to evolve from very short peptide sequences.