Badran, A.H. and Liu, D.R. Nat. Commun. 6, 8425 (2015).

Introducing random mutations into DNA with in vitro techniques is easy, but getting this mutagenized DNA back into cells often is not. Performing mutagenesis directly in cells allows researchers to avoid this bottleneck, but current in vivo methods show only modest mutation rates. To improve these rates, Badran and Liu created and tested several plasmids that include genes affecting mutation frequency. The final plasmid tested, MP6, encodes dominant negative variants of a DNA-proofreading enzyme, a protein that impairs mismatch repair, a cytidine deaminase that increases base transitions and a transcriptional repressor. Escherichia coli carrying MP6 showed a 322,000-fold increase in the mutation rate of their chromosomal DNA compared to wild-type E. coli. MP6 enabled the rapid evolution of an E. coli strain with resistance to many common antibiotics.