Polycomb group proteins (PcG) maintain the transcriptional silence of target genes in cells where these genes must be silenced during Drosophila development. This repression depends on Polycomb group response elements (PREs). Two PcG protein complexes have been isolated from Drosophila embryos: PRC1 and Esc-E(z) complex. In this study, we attempted to determine whether extra sex combs (esc) and Polycomb (Pc) mutations disrupt the functions of GAGA and Zeste, using an Ultrabithorax (Ubx) transgene containing the GAGA or Zeste binding sites. GAGA and Zeste are sequence-specific DNA-binding proteins, which have been previously demonstrated to be trithorax group activators of the homeotic gene Ubx. The Ubx transgene was weakly derepressed in Pc and esc mutants, indicating that Pc and esc interacts with GAGA and Zeste in the promoter of the Ubx transgene.