(236c) Orthogonal Tuning of Gene Expression Noise Using CRISPR-Cas

The noise in gene expression of cells can cause cellular heterogeneity that leads to the failure of antibiotic- and chemo-therapy, as well as synthetic circuits. To study or control the heterogeneity, previous work has tuned gene expression noise by changing the rate of transcription initiation, mRNA degradation, and mRNA translation. However, these methods are invasive: they require changes to the target genetic components. Here, we propose an orthogonal system based on CRISPR-dCas9 to tune gene expression noise and mean independently in a single cell. Specifically, we modulate the protein expression of a reporter gene in Escherichia coli by incorporating CRISPR activation and repression (CRISPRar) simultaneously competing to the same binding site. The CRISPRar uses a single dCas9 that recognizes two different single guide RNAs (sgRNA). We build a library of sgRNA variants with different expression activation and repression strengths. We find that expression noise and mean of a reporter gene can be tuned independently by CRISPRar. Our results suggest that the expression noise is tuned by the competition between two sgRNAs that modulate the binding of the RNA polymerase to a promoter. Our work provides a systematic, quantitative foundation towards designing CRISPR-dCas9 for modulating gene expression noise. The CRISPRar may also change how we tune expression noise at the genomic level. Our work has broad impacts on the study of gene functions, phenotypical heterogeneity, and genetic circuit control.