RecA finds homologous DNA by reduced dimensionality search

Homologous recombination is essential for the accurate repair of double-stranded DNA breaks (DSBs).sup.1. Initially, the RecBCD complex.sup.2 resects the ends of the DSB into 3' single-stranded DNA on which a RecA filament assembles.sup.3. Next, the filament locates the homologous repair template on the sister chromosome.sup.4. Here we directly visualize the repair of DSBs in single cells, using high-throughput microfluidics and fluorescence microscopy. We find that, in Escherichia coli, repair of DSBs between segregated sister loci is completed in 15 [plus or minus] 5 min (mean [plus or minus] s.d.) with minimal fitness loss. We further show that the search takes less than 9 [plus or minus] 3 min (mean [plus or minus] s.d) and is mediated by a thin, highly dynamic RecA filament that stretches throughout the cell. We propose that the architecture of the RecA filament effectively reduces search dimensionality. This model predicts a search time that is consistent with our measurement and is corroborated by the observation that the search time does not depend on the length of the cell or the amount of DNA. Given the abundance of RecA homologues.sup.5, we believe this model to be widely conserved across living organisms. Observations of rapid repair of double-stranded DNA breaks in sister choromosomes in Escherichia coli are consistent with a reduced-dimensionality-search model of RecA-mediated repair.
Author(s): Jakub Wiktor [sup.1] , Arvid H. Gynnå [sup.1] , Prune Leroy [sup.1] , Jimmy Larsson [sup.1] , Giovanna Coceano [sup.2] , Ilaria Testa [sup.2] , Johan Elf [sup.1] Author [...]