Plays a role in the DNA damage response (DDR) pathway by regulating postreplication repair of UV-damaged DNA and genomic stability maintenance (PubMed:25931565). The SLF1-SLF2 complex acts to link RAD18 with the SMC5-SMC6 complex at replication-coupled interstrand cross-links (ICL) and DNA double-strand breaks (DSBs) sites on chromatin during DNA repair in response to stalled replication forks (PubMed:25931565). Promotes the recruitment of the SMC5-SMC6 complex to DNA lesions (PubMed:25931565). Plays a role in SMC5-SMC6 complex recruitment for viral restriction. Forms a complex with SIMC1 and this complex is required to recruit SMC5-SMC6 complex to PML nuclear bodies and sites of viral replication (PubMed:36373674). . This is the function of SLF2 (SMC5/6 complex localization factor 2, ENSG00000119906).