Elongation factor component of the super elongation complex (SEC), a complex required to increase the catalytic rate of RNA polymerase II transcription by suppressing transient pausing by the polymerase at multiple sites along the DNA. Component of the little elongation complex (LEC), a complex required to regulate small nuclear RNA (snRNA) gene transcription by RNA polymerase II and III (By similarity). Plays a role in immunoglobulin secretion in plasma cells: directs efficient alternative mRNA processing, influencing both proximal poly(A) site choice and exon skipping, as well as immunoglobulin heavy chain (IgH) alternative processing. Probably acts by regulating histone modifications accompanying transition from membrane-specific to secretory IgH mRNA expression. Component of the super elongation complex (SEC), at least composed of EAF1, EAF2, CDK9, MLLT3/AF9, AFF (AFF1 or AFF4), the P-TEFb complex and ELL (ELL, ELL2 or ELL3). Component of the little elongation complex (LEC), at least composed of ELL (ELL, ELL2 or ELL3), ZC3H8, ICE1 and ICE2. Interacts with AFF4; the interaction is direct and leads to stabilize ELL2 and prevent ELL2 ubiquitination. Interacts with EAF1 and EAF2 (By similarity). Ubiquitinated by SIAH1, leading to its degradation by the proteasome. Interaction with AFF4 stabilizes ELL2 and prevents ELL2 ubiquitination (By similarity). Belongs to the ELL/occludin family.