Identifying and characterizing SCRaMbLEd synthetic yeast using ReSCuES

SCRaMbLE is a novel system implemented in the synthetic yeast genome, enabling massive chromosome rearrangements to produce strains with a large genotypic diversity upon induction. Here we describe a reporter of SCRaMbLEd cells using efficient selection, termed ReSCuES, based on a loxP-mediated switch of two auxotrophic markers. We show that all randomly isolated clones contained rearrangements within the synthetic chromosome, demonstrating high efficiency of selection. Using ReSCuES, we illustrate the ability of SCRaMbLE to generate strains with increased tolerance to several stress factors, such as ethanol, heat and acetic acid. Furthermore, by analyzing the tolerant strains, we are able to identify ACE2, a transcription factor required for septum destruction after cytokinesis, as a negative regulator of ethanol tolerance. Collectively, this work not only establishes a generic platform to rapidly identify strains of interest by SCRaMbLE, but also provides methods to dissect the underlying mechanisms of resistance.