Core component of the SMC5-SMC6 complex, a complex involved in DNA double-strand breaks by homologous recombination. The complex may promote sister chromatid homologous recombination by recruiting the SMC1-SMC3 cohesin complex to double-strand breaks. The complex is required for telomere maintenance via recombination in ALT (alternative lengthening of telomeres) cell lines and mediates sumoylation of shelterin complex (telosome) components which is proposed to lead to shelterin complex disassembly in ALT-associated PML bodies (APBs). Required for recruitment of telomeres to PML nuclear bodies. SMC5-SMC6 complex may prevent transcription of episomal DNA, such as circular viral DNA genome (PubMed:26983541). Forms a heterodimer with SMC5 (PubMed:11408570). Component of the SMC5-SMC6 complex which consists at least of SMC5, SMC6, NSMCE2, NSMCE1, NSMCE4A or EID3 and NSMCE3 (PubMed:18086888). Interacts with NSMCE1 (PubMed:14701739). Interacts with NSMCE2 (PubMed:16055714). Interacts with SLF1 (PubMed:25931565). Interacts with SLF2 (PubMed:25931565). Interacts with RAD18 (PubMed:25931565). (Microbial infection) SMC5-SMC6 complex interacts with Hepatitis B X protein. Colocalizes with SMC5 on the X-Y chromosome pair within the sex vesicle during late pachytene/diplotene (By similarity). Localizes to PML nuclear bodies in ALT cell lines (PubMed:17589526). Associates with chromatin (PubMed:25931565). Accumulates with RAD18 and the SLF1-SLF2 complex at replication-coupled DNA interstrand repair and DNA double-strand breaks (DSBs) sites on chromatin in a ubiquitin-dependent manner (PubMed:25931565). Localizes in interchromatin granule clusters (PubMed:11408570). Widely expressed (PubMed:11408570). Strongly expressed in testis (PubMed:11408570). The flexible hinge domain, which separates the large intramolecular coiled coil regions, allows the heterotypic interaction with the corresponding domain of SMC5, forming a V-shaped heterodimer. Phosphorylated. Sumoylated by NSMCE2/MMS21. Ubiquitinated. (Microbial infection) SMC5-SMC6 complex is degraded by the activity of Hepatitis B X protein. Belongs to the SMC family. SMC6 subfamily. Contaminating sequence. Potential poly-A sequence.