An experimental solution for the Luria–Delbrück fluctuation problem in measuring hypermutation rates

A cell line harboring all trans-acting elements necessary for hypermutation was transfected with a plasmid harboring the major cis-acting elements plus a green fluorescent protein gene containing a premature chain-termination codon. Transfected cells do not fluoresce unless the stop codon reverts. When a sizable cell population is purged of revertants by sorting, the frequency of mutants increases linearly with time, and there is no Luria–Delbrück fluctuation effect. Moreover, as mutant frequencies seemed to vary less than cell numbers in replicate cultures, it is suggested that hypermutation might not be coupled closely to cell division.