N-terminal sub-domain of the Rel homology domain (RHD) of the arthropod protein Dorsal
Proteins containing the Rel homology domain (RHD) are metazoan transcription factors. The RHD is composed of two structural sub-domains; this model characterizes the N-terminal RHD sub-domain of the arthropod Dorsal and Dif (Dorsal-related immunity factor), and similar proteins. Dorsal and Dif are Rel-like transcription factors, which play roles in mediating innate immunity in Drosophila. They are activated via the Toll pathway. Cytoplasmic Dorsal/Dif are inactivated via forming a complex with Cactus, the Drosophila homologue of mammalian I-kappa B proteins. In response to signals, Cactus is degraded and Dorsal/Dif can be transported into the nucleus, where they act as transcription factors. Dorsal is also an essential gene in establishing the proper dorsal/ventral polarity in the developing embryo.