PSIP1 (also known as LEDGF) is co-immunoprecipitated with MEN1-bound MLL2 complexes (van Nuland et al. 2013). Although the LEDGF binding motif (LBM) that is present in KMT2A is missing in KMT2B (Huang et al. 2012), PSIP1 can directly interact with MEN1 (Huang et al. 2012). Based on quantitative studies in HeLa cells, all PSIP1-containing MLL1/MLL2 complexes contain MEN1, but only about 25% of MEN1-containing MLL1/MLL2 complexes contain PSIP1 (van Nuland et al. 2013). PSIP1 appears to be more prevalent in MLL2:MEN1 complexes than in MLL1:MEN1 complexes (van Nuland et al. 2013). HCFC2 has been found to be co-immunoprecipitated with PSIP1, so it is possible that a portion of MLL2 complexes with MEN1 and PSIP1 also include HCFC1 or HCFC2 (van Nuland et al. 2013).