Visualizing high error levels during gene expression in living bacterial cells Mor Meyerovich1, Gideon Mamou1, and Sigal Ben-Yehuda2 Department of Microbiology and Molecular Genetics, Institute for Medical Research, Israel-Canada, Hebrew University–Hadassah Medical School, Hebrew University of Jerusalem, 91120 Jerusalem, Israel Edited* by Susan Gottesman, National Cancer Institute, Bethesda, MD, and approved May 20, 2010 (received for review November 19, 2009) Tomonitor inaccuracy in gene expression in living cells, wedesigned an experimental system in the bacterium Bacillus subtilis whereby spontaneous errors can be visualized and quantified at a single-cell level.Our strategywas to introducemutations into a chromosomally encoded gfp allele, such that errors in protein production are reported in real time by the formation of fluorescent GFP molecules. The data reveal that the amount of errors can greatly exceed previous estimates, and that the error rate increases dramatically at lower temperatures and during stationary phase. Furthermore, we demonstrate that when facing an antibiotic threat, an increase in error level is sufficient to allow survival of bacteria carrying a mutated antibiotic-resistance gene. We propose that bacterial gene expression is error prone, frequently yielding protein molecules that differ slightly from the sequence specified by their DNA, thus generating a cellular reservoir of nonidentical protein molecules. This variation may be a key factor in increasing bacterial fitness, expanding the capability of an isogenic population to face environmental challenges. Bacillus subtilis | translational errors | variations in living cells | translation fidelity DNA is duplicated with remarkable fidelity to ensure that accurate genetic information is transmitted fromone generation to the next. This information is passed from DNA to RNA and from RNA to protein during gene expression; however, the accuracy of these downstream events is relatively less…