Correction of deletions in mammalian cells by gene conversion.

We have constructed substrates to study the conversion of deletions in mammalian cells both extrachromosomally and after the stable integration of the substrates into the chromosome. These substrates were designed to study gene conversion without the complication of reciprocal recombination events. The substrates contain insertion or deletion mutations of the neomycin resistance gene (neo) and an internal, homologous fragment of the neo gene (neo-526), such that gene conversion from neo-526 to the mutated neo gene restores a functional neo gene. We have shown that extrachromosomally insertions of 10 bp or deletions of 22 or 167 bp are converted to wild-type at similar frequencies (1-6 X 10(-4)). Chromosomal gene conversion occurred at frequencies of about 10(-6)-10(-7) per cell generation. As expected from the experimental design, all recombination events analyzed in mammalian cells using these substrates appear to be due to gene conversion.