The Notch (N) pathway defines an evolutionarily conserved cell signaling mechanism that governs cell fate choices through local cell interactions. The ankyrin repeat region of the Notch receptor is essential for signaling and has been implicated in the interactions between Notch and two intracellular elements of the pathway: Deltex (Dx) and Suppressor of Hairless (Su(H)). Here we examine directly the function of the Notch cdc10/ankyrin repeats (ANK repeats) by transgenic and biochemical analysis. We present evidence implicating the ANK repeats in the regulation of Notch signaling through homotypic interactions. In vivo expression of the Notch ANK repeats reveals a cell non-autonomous effect and elicits mutant phenotypes that indicate the existence of novel downstream events in Notch signaling. These signaling activities are independent of the known effector Su(H) and suggest the existence of yet unidentified Notch pathway components.
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