UC San Diego

The innate immune system of Drosophila melanogaster is a well-studied model of evolutionarily conserved innate immunity. The humoral branch of Drosophila immunity is regulated by the Toll and Imd pathways, which signal through the NF-[kappa]B family members Dif and Relish, respectively. Here is presented evidence that ?B motifs, the target DNA sequences of NF-[kappa]B factors, direct pathway-specific gene expression of innate immune loci by determining the binding of Dif and Relish to the promoters of target genes. Using a combination of immune gene luciferase reporters, bioinformatic analyses, and in vitro binding studies, the regulatory code through which [kappa]B motifs direct this pathway specific expression was deciphered. The binding specificity of [kappa]B motifs is determined by the number of guanine bases in the 5' G cluster, and the number of A or T bases between the 5' G cluster and the 3' C cluster. Examination of four immune responsive genes led to the discovery that cooperative interaction of multiple [kappa]B motifs is a crucial determinant of pathway responsiveness. Multiple [kappa]B motifs responsive to the same pathway cooperatively increase the response to that pathway, and multiple motifs responsive to different pathways allows a synergistic response to simultaneous activation of both pathways. Together, these studies elucidate the mechanism by which [kappa]B motifs direct binding by particular Drosophila NF -[kappa]B family members and thereby regulate the induction of immune responsive genes