Seeing mutations in living cells.
BACKGROUND
Evolution depends on mutations: rare errors in the transmission of genetic information. Experimentally, mutations have been found by detecting altered phenotypes or sequencing complete genomes, but most mutations do not have overt phenotypes, and sequencing is expensive and has limited time resolution. The major source of mutations is DNA replication errors. Nearly all mistakes in DNA replication are detected and repaired by the mismatch repair machinery.


RESULTS
We use a functional, fluorescently labeled derivative of one of the key mismatch repair proteins (MutL) to see and count the small fraction of errors in Escherichia coli that does not get repaired and is converted into stable mutations by the next round of DNA replication. Over a 300-fold range, there is a linear relationship between the frequency of fluorescent foci and the genetically measured mutation frequency, and the mean frequency of fluorescent foci agrees well with estimates of the global mutation rate.


CONCLUSIONS
We describe a method for detecting the majority of genomic mutations emerging in living cells, independently of their potential phenotype. The distribution of emerging mutations per cell is roughly Poisson distributed, suggesting that all the cells in the population have roughly the same mutation rate.
Elez
Marina
M
University Paris-Descartes Medical School, Inserm Unit 1001, 75730 Paris Cedex 15, France.
Murray
Andrew W
AW
Bi
Li-Jun
LJ
Zhang
Xian-En
XE
Matic
Ivan
I
Radman
Miroslav
M
D000251:Adenosine Triphosphatases / Q000032:analysis; D004260:DNA Repair; D004261:DNA Replication; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000032:analysis; D049452:Green Fluorescent Proteins / Q000032:analysis; D008957:Models, Genetic; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein / Q000032:analysis; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000032:analysis; D012293:Rifampin / Q000494:pharmacology
D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli; D012293:Rifampin