SMC protein RecN drives translocation and remodelling of RecA filament for homology search

While the molecular repertoire of the homologous recombination pathway is well studied, the search mechanism that enables recombination between distant homologous regions is poorly understood. Here, we follow the dynamics of the recombinase RecA, an essential component of homology search, after induction of a single double-strand break on the Caulobacter chromosome. We find that the RecA-nucleoprotein filament translocates in a directional manner in the cell, undergoing several pole-to-pole traversals, until homology search is complete. Simultaneously, the filament undergoes dynamic remodelling; both translocation and dynamic remodelling are contingent on the action of the SMC protein RecN via its ATPase cycle. We provide a stochastic description of RecN regulated changes in filament length during translocation via modulation of RecA assembly-disassembly. Together, the observed RecN driven RecA dynamics points to a novel optimal search strategy.