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. Strongly expressed in heart, brain, placenta, lung, liver, skeletal muscle, kidney, pancreas, spleen, prostate, testis, small intestine and colon. Poorly expressed in thymus. Belongs to the EAF family.