The proliferating cell nuclear antigen (PCNA) is a nuclear protein whose expression is high at S phase of the cell cycle. Raf-1 plays an important role in the signaling process in cell proliferation and differentiation. The binding consensus for homeodomain proteins are located in the regulatory regions of the Drosophila PCNA and raf genes. The homeodomain protein Ftz is shown to be a site-dependent activator of transcription. Another homeodomain protein, the engrailed (en) gene product, competes for homeodomain-binding sites and counteracts ftz activation. In this study, to investigate a possibility that the expression of PCNA and D-raf genes is regulated by these homeodomain proteins, we examined effects of the Ftz and the Engrailed on expression of the Drosophila raf and PCNA genes by transient expression assays in Drosophila Kc cells using the reporter plasmids, p5-168DPCNACAT and p5-878DrafCAT, and the effector plasmids, pAct5c-ftz and pAct5C-en.