Acts as a transcriptional transactivator of ELL and ELL2 elongation activities. 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). Interacts with ELL and ELL2 (By similarity). Belongs to the EAF family.