Searching for homology:
in vivo dynamics of bacterial recombination

Double-strand breaks (DSBs) are a lethal form of DNA damage, that if left unrepaired, can lead to genome instability in cells. Cells across domains of life can repair DSBs using an error-free mechanism called homologous recombination. This pathway requires an intact copy of duplex DNA that serves as template for repair. A key step in recombination is the process of homology search, where a DSB site locates the recombination substrate within the nuclear or cellular volume. This is orchestrated via the action of a conserved recombinase called RecA (in bacteria). RecA nucleates and forms a pre-synaptic filament at a break site. This nucleoprotein filament then engages in micro-homology sampling and strand invasion to identify and pair with the homologous template. More recently, our in vivo study tracking the dynamics of the RecA filament during homology search in Caulobacter revealed that the filament is dynamic and mobile; RecA localizations were observed to engage in directional movement within the cell. This translocation was accompanied by RecA filament length remodeling, and occurred in a template-independent manner. Importantly, the Structural Maintenance of Chromosome protein RecN, was essential to drive these dynamics. In the absence of the same, no repair was observed. Thus, homology search during recombination entails RecN-driven directional translocation and remodeling of a dynamic RecA filament. The underlying molecular mechanism driving such mobility remains an exciting open question. Presently, we are probing key features that directly/ indirectly influence the observed RecA dynamics.