This is the conserved middle region of a family of proteins referred to as cactins. The region contains two of three predicted coiled-coil domains. Most members of this family have a CactinC_cactus Pfam:PF09732 domain at the C-terminal end. Upstream of Mid_cactin in Drosophila members are a serine-rich region, some non-typical RD motifs and three predicted bipartite nuclear localisation signals, none of which are well-conserved. Cactin associates with IkappaB-cactus as one of the intracellular members of the Rel (NF-kappaB) pathway which is conserved in invertebrates and vertebrates. In mammals, this pathway controls the activities of the immune and inflammatory response genes as well as viral genes, and is critical for cell growth and survival. In Drosophila, the Rel pathway functions in the innate cellular and humoral immune response, in muscle development, and in the establishment of dorsal-ventral polarity in the early embryo [1].

1: Cactin, a conserved protein that interacts with the Drosophila IkappaB protein cactus and modulates its function. Lin P, Huang LH, Steward R; Mech Dev. 2000;94:57-65. PMID:10842059