Adapter protein able to interact with different proteins and involved in different biological processes. Mediates the interaction between the error-prone DNA polymerase zeta catalytic subunit REV3L and the inserter polymerase REV1, thereby mediating the second polymerase switching in translesion DNA synthesis. Translesion DNA synthesis releases the replication blockade of replicative polymerases, stalled in presence of DNA lesions. Component of the shieldin complex, which plays an important role in repair of DNA double-stranded breaks (DSBs). During G1 and S phase of the cell cycle, the complex functions downstream of TP53BP1 to promote non-homologous end joining (NHEJ) and suppress DNA end resection. Mediates various NHEJ-dependent processes including immunoglobulin class-switch recombination, and fusion of unprotected telomeres. May also regulate another aspect of cellular response to DNA damage through regulation of the JNK-mediated phosphorylation and activation of the transcriptional activator ELK1. Inhibits the FZR1- and probably CDC20-mediated activation of the anaphase promoting complex APC thereby regulating progression through the cell cycle. Regulates TCF7L2-mediated gene transcription and may play a role in epithelial-mesenchymal transdifferentiation. Homooligomer (By similarity). Heterodimer with REV3L (By similarity). This dimer forms the minimal DNA polymerase zeta complex (Pol-zeta2), with REV3L bearing DNA polymerase catalytic activity, although its activity is very low in this context (By similarity). Component of the tetrameric Pol-zeta complex (Pol-zeta4), which consists of REV3L, MAD2L2, POLD2 and POLD3; Pol-zeta4 is the fully active form of DNA polymerase zeta (By similarity). Component of the shieldin complex, consisting of SHLD1, SHLD2, SHLD3 and MAD2L2/REV7. Within the complex, SHLD2 forms a scaffold which interacts with a SHLD3-MAD2L2 subcomplex via its N-terminus, and with SHLD1 via its C-terminus (By similarity). Interacts with REV1 (PubMed:14657033). Interacts with ADAM9 (By similarity). Interacts with CHAMP1 (By similarity). Interacts with FZR1 (in complex with the anaphase promoting complex APC) (By similarity). May interact with CDC20 (By similarity). Interacts with RAN (By similarity). Interacts with ELK1; the interaction is direct and recruits MAD2L2 to ELK1-specific promoters (By similarity). May interact with the JNK kinases MAPK8 and/or MAPK9 to stimulate ELK1 phosphorylation and transcriptional activity upon DNA damage (By similarity). Interacts with TCF7L2; prevents its binding to promoters and negatively modulates its transcriptional activity (By similarity). Interacts with YY1AP1 (By similarity). Interacts with PRCC; the interaction is direct (By similarity). Interacts with POGZ (By similarity). Recruited to sites of chromosomal double-stranded breaks during G1 and S phase of the cell cycle.