Component of the MMS22L-TONSL complex, a complex that promotes homologous recombination-mediated repair of double-strand breaks (DSBs) at stalled or collapsed replication forks. The MMS22L-TONSL complex is required to maintain genome integrity during DNA replication. It mediates the assembly of RAD51 filaments on single-stranded DNA (ssDNA): the MMS22L-TONSL complex is recruited to DSBs following histone replacement by histone chaperones and eviction of the replication protein A complex (RPA/RP-A) from DSBs. Following recruitment to DSBs, the TONSL-MMS22L complex promotes recruitment of RAD51 filaments and subsequent homologous recombination. Within the complex, TONSL acts as histone reader, which recognizes and binds newly synthesized histones following their replacement by histone chaperones. Specifically binds histone H4 lacking methylation at 'Lys-20' (H4K20me0) and histone H3.1. Component of the MMS22L-TONSL complex, a complex at least composed of MMS22L and TONSL/NFKBIL2. Interacts with the MCM complex, the FACT complex and the RPA complex. Interacts with MCM5; the interaction is direct. Binds histones, with a strong preference for histone H3.1 (histones H3.1 and H3-4/H3.1t). Interacts (via ANK repeats) with histone H4; specifically binds histone H4 lacking methylation at 'Lys-20' (H4K20me0). May interact with DNAJC9; the interaction seems to be histone-dependent. Mainly nuclear. Localizes to DNA damage sites, accumulates at stressed replication forks. Recruited to stalled or collapsed replication forks following histone replacement by histone chaperones ASF1A and the CAF-1 complex: TONSL acts as histone reader that recognizes and binds newly synthesized histones. The ANK repeats mediate the interaction with the MCM complex and histones, while the LRR repeats mediate the interaction with MMS22L. Belongs to the Tonsoku family.