More recently, the wealth of molecular data on homeotic genes have demonstrated that they encode sequence-specific DNA-binding proteins (Beachy et al., 1988; Muller et al., 1988) capable of activating or repressing transcription from a variety of reporter gene constructs in vitro (Thali et al., 1988; Krasnow et al., 1989; Winslow et al., 1989).