E3 ubiquitin-protein ligase that regulates ubiquitin-dependent retention of repair proteins on damaged chromosomes. Recruited to sites of DNA damage in response to ionizing radiation (IR) and facilitates the assembly of UBE2N and RNF8 promoting DNA damage-induced formation of 'Lys-63'-linked ubiquitin chains. Acts as a mediator of binding specificity between UBE2N and RNF8. Involved in the maintenance of RNF168 levels. E3 ubiquitin-protein ligase that promotes the ubiquitination and proteasomal degradation of XPA which influences the circadian oscillation of DNA excision repair activity. By controlling the steady-state expression of the IGF1R receptor, indirectly regulates the insulin-like growth factor receptor signaling pathway. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts (when phosphorylated at Thr-4829 and sumoylated) with RNF8 (via FHA domain); this interaction increases after ionising radiation (IR) treatment. Interacts with XPA. Interacts with NEURL4. Via its interaction with NEURL4, may indirectly interact with CCP110 and CEP97. Recruited to sites of DNA damage in response to ionising radiation (IR) via its interaction with RNF8. May loose association with centrosomes during mitosis. Highest levels are found in brain and testis with lower levels in heart, lung, liver, skeletal muscle and kidney. Little expression detected in spleen. The ZZ-type zinc finger mediates binding to SUMO1, and at low level SUMO2. The RCC1 repeats are grouped into three seven-bladed beta-propeller regions. Phosphorylation at Thr-4829 is required for interaction with RNF8. Sumoylated with SUMO1 by PIAS4 in response to double-strand breaks (DSBs), promoting the interaction with RNF8. Defects in Herc2 are the cause of the runty, jerky, sterile phenotype (rjs), also known as the juvenile development and fertility phenotype (jfd2), which is characterized by reduced size, jerky gait, fertility problems including spermatocyte and oocyte abnormalities, defective maternal behavior and reduced lifespan with juvenile lethality.