Codon usage influences fitness through RNA toxicity

To study the molecular mechanisms of toxicity caused by GFP mRNA overexpression, we aimed to evolve genetic suppressors of toxicity. We selected several GFP constructs that showed both strong toxicity and moderate or high GFP fluorescence, and plated bacteria containing these constructs on LB agar plates with IPTG and ampicillin. We observed a number of large white colonies that apparently expressed no GFP, and smaller bright green colonies producing high amounts of the GFP protein. We selected 22 evolved strains and the parental strain for genome sequencing,