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. May also play a role in signal transduction in response to DNA damage. May regulate the activation of the anaphase promoting complex APC thereby regulating progression through the cell cycle. 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 (By similarity). Through transcriptional regulation may play a role in epithelial-mesenchymal transdifferentiation. Homooligomer. Interacts with REV1. Interacts with FZR1 (in complex with the anaphase promoting complex APC). May interact with CDC20 (By similarity). Heterodimer with REV3L. 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. 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. 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.