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. Component of the MMS22L-TONSL complex. Binds histones, with a strong preference for histone H3.1 (histones H3.1 and H3-4/H3.1t). 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: TONSL acts as histone reader that recognizes and binds newly synthesized histones. Tonsl deficiency causes growth deficits, vertebral abnormalities, reduced neutrophil numbers, and death at early stages of larvae development. Belongs to the Tonsoku family. Extended N-terminus.