ORIGINS OF IMMUNITY - RELISH, A COMPOUND REL-LIKE GENE IN THE ANTIBACTERIAL DEFENSE OF DROSOPHILA

NF-kappa B/Rel transcription factors are central regulators of mammali an immunity and are also implicated in the induction of cecropins and other antibacterial peptides in insects. We identified the gene for Re lish, a compound Drosophila protein that, like mammalian p105 and p100 , contains both a Rel homology domain and an I kappa B-like domain. Re lish is strongly induced in infected flies, and it can activate transc ription from the Cecropin A1 promoter. A Relish transcript is also det ected in early embryos, suggesting that it acts in both immunity and e mbryogenesis. The presence of a compound Rel protein in Drosophila ind icates that similar proteins were likely present in primordial immune systems and may serve unique signaling functions.