SIII, also known as elongin, is a general transcription elongation factor that increases the RNA polymerase II transcription elongation past template-encoded arresting sites. Subunit A is transcriptionally active and its transcription activity is strongly enhanced by binding to the dimeric complex of the SIII regulatory subunits B and C (elongin BC complex) (By similarity). In embryonic stem cells, the elongin BC complex is recruited by EPOP to Polycomb group (PcG) target genes in order generate genomic region that display both active and repressive chromatin properties, an important feature of pluripotent stem cells (By similarity). Core component of multiple cullin-RING-based ECS (ElonginB/C-CUL2/5-SOCS-box protein) E3 ubiquitin-protein ligase complexes, which mediate the ubiquitination of target proteins. This includes the von Hippel-Lindau ubiquitination complex CBC(VHL). By binding to BC-box motifs it seems to link target recruitment subunits, like VHL and members of the SOCS box family, to Cullin/RBX1 modules that activate E2 ubiquitination enzymes. A number of ECS complexes (containing either KLHDC2, KLHDC3, KLHDC10, APPBP2, FEM1A, FEM1B or FEM1C as substrate-recognition component) are part of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation. Protein modification; protein ubiquitination. Heterotrimer of an A (ELOA, ELOA2 or ELOA3P), ELOB and ELOC subunit (By similarity). The elongin BC complex interacts with EPOP; leading to recruit the elongin BC complex to Polycomb group (PcG) target genes, thereby restricting excessive activity of the PRC2/EED-EZH2 complex (By similarity). Part of E3 ubiquitin ligase complexes with CUL5 or CUL2, RBX1 and a substrate adapter protein that can be either ASB2, KLHDC2, KLHDC3, KLHDC10, APPBP2, FEM1A, FEM1B, FEM1C, SOCS1, SOCS5, ELOA, VHL or WSB1. The elongin BC complex is part of a complex with VHL and hydroxylated HIF1A. Part of an E3 ubiquitin-protein ligase complex including ZYG11B, CUL2 and Elongin BC. Part of an E3 ubiquitin-protein ligase complex including ZER1, CUL2 and Elongin BC. Interacts with VHL. Interacts with TMF1. Interacts with SPSB1. Interacts with SPSB1. Interacts with KLHDC10; which may be an E3 ubiquitin ligase complex substrate recognition component. Interacts with NOS2 in the presence of SPSB1 or SPSB2 or SPSB4 (By similarity). Ubiquitinated by the DCX(AMBRA1) complex, leading to its degradation by the proteasome. Belongs to the SKP1 family.