UBC13-mediated template switching promotes replication stress resistance in FBH1-deficient cells

The proper resolution of DNA damage during replication is essential for genome stability. FBH1, a UvrD, helicase plays crucial roles in the DNA damage response. FBH1 promotes double strand break formation and signaling in response to prolonged replication stress to initiate apoptosis. Human FBH1 regulates RAD51 to inhibit homologous recombination. A previous study suggested that mis-regulation of RAD51 may contribute to replication stress resistance in FBH1-deficient cells, but the underlying mechanism remains unknown. Here, we provide direct evidence that RAD51 promotes replication stress resistance in FBH1-deficient cells. We demonstrate inhibition of RAD51 using the small molecule, B02, partially rescues double strand break signaling in FBH1-deficient cells. We show that inhibition of only the strand exchange activity of RAD51 rescues double strand break signaling in FBH1 knockout cells. Finally, we show that depletion of UBC13, a E2 protein that promotes RAD51-dependent template switching, rescues double strand break formation and signaling sensitizing FBH1- deficient cells to replication stress. Our results suggest FBH1 regulates template switching to promote replication stress sensitivity. ### Competing Interest Statement The authors have declared no competing interest.