POU domain of BmPOUM2 and homeobox domain and LCR2 of BmAbd-A were essential for the protein interaction. Six amino acids in POU-specific domain and eight amino acids in homeobox domain were critical for the protein interaction. BmAbd-A bound to Hox CRE and BmPOUM2 bound to POU CRE of BmWCP4 promoter, co-regulating the gene expression.