Oligomerisation of Tube and Pelle leads to nuclear localisation of Dorsal

In the Drosophila embryo the nuclear localisation of Dorsal, a member of th e Rel family, is regulated by an extracellular signal, which is transmitted to the interior of the egg cell by a cascade of proteins involving the nov el protein Tube and the protein kinase Pelle. Here we analyse the activatio n mechanism of Tube and Pelle and the interaction between these two compone nts. We show that both proteins, although having different biochemical acti vities, are activated by the same mechanism. Membrane association alone is not sufficient, but oligomerisation is required for full activation of Tube and Pelle. By deletion analysis we determined the domains of Tube and Pell e mediating the physical interaction and the signalling to downstream compo nents. In order to investigate the link between Pelle and the target of the signalling cascade, the Dorsal/Cactus complex, we isolated and characteris ed the novel, but evolutionary conserved protein Pellino, which associates with the kinase domain of Pelle. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.