| dc.description.abstract | DNA replication is frequently challenged by obstacles that require accurate and timely repair to maintain genome stability. In some cases, repair mechanisms are coupled with the replisome to process the damaged DNA. One such mechanism is known as replication fork reversal. Fork reversal involves the physical remodeling of forks to possibly help stabilize and allow for error-free repair of stalled forks. Although potentially a useful replication stress response mechanism, unregulated fork reversal can cause genome instability. Fork reversal requires SWI/SNF2 family translocases including SMARCAL1, ZRANB3, or HLTF. In addition, fork reversal requires a single-strand DNA (ssDNA) binding protein, RAD51. How RAD51 promotes fork reversal is not known. RAD51 also facilitates homologous recombination repair of double-strand breaks and protects reversed forks from nuclease degradation. Our lab recently identified a ssDNA binding protein related to RPA called RADX that localizes to active and stalled replication forks. Biochemically, RADX binds to and destabilizes RAD51 nucleofilaments. My dissertation work focused on understanding the functions of RADX and RAD51 at elongating and stalled replication forks. I discovered that RADX can either inhibit or promote fork reversal depending on replication stress levels. At elongating forks, RADX inhibits fork reversal thereby preventing fork slowing and collapse. Paradoxically, in the presence of persistent replication stress, RADX localizes to stalled forks to help generate reversed fork structures. Consequently, RADX increases SMARCAL1-dependent fork reversal in cases where RAD51 binding to model substrates is inhibitory. RADX generates these context-dependent effects by directly binding ssDNA and RAD51 to generate a metastable RAD51 filament at stalled forks. This difference in phenotypes at elongating versus stalled forks may be due to differences in the amount and persistence of ssDNA. Thus, RADX confines fork reversal at persistently stalled forks to maintain genome stability. | |
