Binds KMT2A/MLL1. Component of the MLL1/MLL complex, at least composed of KMT2A/MLL1, ASH2L, RBBP5, DPY30, WDR5, MEN1, HCFC1 and HCFC2 (PubMed:15199122). Interacts with TASOR (By similarity). Highly expressed in testis. Detected at lower levels in spleen, thymus, prostate, ovary, small intestine and colon.