Involved in the homologous recombination repair (HRR) pathway of double-stranded DNA, thought to repair chromosomal fragmentation, translocations and deletions. Part of the RAD21 paralog protein complex CX3 which acts in the BRCA1-BRCA2-dependent HR pathway. Upon DNA damage, CX3 acts downstream of RAD51 recruitment; the complex binds predominantly to the intersection of the four duplex arms of the Holliday junction (HJ) and to junctions of replication forks. Involved in HJ resolution and thus in processing HR intermediates late in the DNA repair process; the function may be linked to the CX3 complex and seems to involve GEN1 during mitotic cell cycle progression. Part of a PALB2-scaffolded HR complex containing BRCA2 and RAD51C and which is thought to play a role in DNA repair by HR. Plays a role in regulating mitochondrial DNA copy number under conditions of oxidative stress in the presence of RAD51 and RAD51C (By similarity). Interacts with RAD51C and RAD51. Part of the CX3 complex consisting of RAD51C and XRCC3; the complex has a ring-like structure arranged into a flat disc around a central channel; CX3 can interact with RAD51 in vitro. Forms a complex with FANCD2, BRCA2 and phosphorylated FANCG. Interacts with SWSAP1 and ZSWIM7; involved in homologous recombination repair. Interacts directly with PALB2 which may serve as a scaffold for a HR complex containing PALB2, BRCA2, RAD51C, RAD51 and XRCC3 (By similarity). Accumulates in discrete nuclear foci prior to DNA damage, and these foci persist throughout the time course of DNA repair. Belongs to the RecA family. RAD51 subfamily.