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Letter

Nature Genetics 31, 419–423 (1 August 2002) | doi:10.1038/ng938

PP1 binds Sara and negatively regulates Dpp signaling in Drosophila melanogaster

Daimark Bennett & Luke Alphey

In signaling involving the transforming growth factor-β (TGF-β) superfamily of proteins, ligand binding brings the constitutively active type II receptor kinase into close proximity to its substrate, the type I receptor kinase, which it then activates by phosphorylation. The type I receptor kinase in turn phosphorylates one of the Smad family of transcription factors, which translocates to the nucleus and regulates gene expression.