INTERSPECIFIC COMPARISONS REVEAL CONSERVED FEATURES OF THE DROSOPHILATOLL PROTEIN

The Toll gene of Drosophilia melanogaster produces a transmembrane cel l adhesion protein that is required to establish the dorso-ventral axi s of the embryo. The Toll protein's extracellular domain contains Leu- rich repeats (LRR), implicated in intermolecular interactions, and its large intracellular domain transduces a signal that eventually reache s the nucleus. Here, we report amino-acid (aa) sequences encoded by th e Toll genes of D.pseudoobscura a and D.virilis, and two distinct Toll -like genes of the grasshopper, Schistocerca americana. Interspecific comparisons show a Toll-specific subfamily of LRR, and a strikingly hi gh degree of conservation in the cytoplasmic domain. Interestingly, ma ny aa residues conserved among the insect Toll-like cytoplasmic domain s are also conserved in mammalian and avian type-I interleukin-1 recep tors and the hypothetical product of a transcript, MyD88, found in mur ine myeloid cells. Thus, we identify a set of conserved aa in the cyto plasmic domain which might be used in a signal-transduction pathway sh ared by invertebrates and vertebrates.