Cytosine deamination to uracil occurs frequently in cellular DNA. In vitro, RNA 
polymerase efficiently inserts adenine opposite to uracil, resulting in G to A 
base substitutions. In vivo, uracil could potentially alter transcriptional 
fidelity, resulting in production of mutant proteins. This study demonstrates 
that in nondividing Escherichia coli cells, a DNA template base replaced with 
uracil in a stop codon in the firefly luciferase gene results in conversion of 
inactive to active luciferase. The level of transcriptional base substitution is 
dependent on the capacity to repair uracil. These results provide evidence for a 
DNA damage-dependent, transcription-driven pathway for generating mutant 
proteins in nondividing cells.