Trans-acting factor that binds to glucocorticoid modulatory elements (GME) present in the TAT (tyrosine aminotransferase) promoter and increases sensitivity to low concentrations of glucocorticoids. Binds also to the transferrin receptor promoter. Essential auxiliary factor for the replication of parvoviruses. Homodimer, and heterodimer of GMEB1 and GMEB2. GMEB1 and GMEB2 form the parvovirus initiator complex (PIF). Interacts with the glucocorticoid receptor (NR3C1). May interact with CREB-binding protein (CBP). May be also cytoplasmic. Expressed in peripheral blood lymphocytes and fetal liver. Expressed preferentially in reproductive and/or developmentally important cells, such as testis, placenta, bone marrow and fetal tissues.