HMG boxes of DSP1 protein interact with the Rel homology domain of transcription factors

Formation of the dorsoventral axis in Drosophila melanogaster is mediated t hrough control of the expression of several genes by the morphogen Dorsal. In the ventral part of the embryo Dorsal activates twist and represses ren amongst others, Recently, several proteins have been shown to assist Dorsal in the repression of ten, one of which is DSP1, a HMG box protein that was isolated as a putative co-repressor of Dorsal. In this report we used a DS P1 null mutant to ascertain in vivo the involvement of DSP1 in Dorsal-media ted repression of ten but not in the activation of twist. We show that Dors al has the ability to interact with DSP1 in vitro as well as with rat HMG1. Using truncated versions of the proteins we located the domains of interac tion as being the HMG boxes for DSP1 and HMG1 and the Rel domain for Dorsal , Finally, studies of the ten DNA binding properties of Dorsal and another related Rel protein (Gambif1 from Anopheles gambiae) revealed that their DN A binding affinities were increased in the presence of DSP1 and HMG1.