Ci protein, short for Cubitus interruptus, is a
zinc finger containing
transcription factor[1] involved in the
Hedgehogsignaling pathway.[2] In the absence of a signal to the Hedgehog signaling pathway, the Ci protein is cleaved and destroyed in
proteasomes. It isn't, however, completely destroyed; part of the protein survives and acts as a
repressor in the
nucleus, keeping genes responsive to the Hedgehog signal silent.
Degradation of Ci
The degradation of Ci protein depends on a large multiprotein complex, which contains a serine/threonine
kinase of unknown function, an
anchoring protein that binds to
microtubules (to keep the Ci protein out of the nucleus) and an adaptor protein.[3] When the Hedgehog signaling pathway is turned on, the Ci
proteolysis is suppressed and the unprocessed CI protein enters the nucleus, where it activates the transcription of its target genes. Ci undergoes complete or partial degradation in the cells, the detailed molecular mechanism is poorly understood. It has been reported that an AAA ATPase Ter94 complex and K11/K48 ubiquitin chains are involved in the selection of Ci degradation.[4]
Target genes
The Wingless protein in
Drosophila, which is crucial to the embryogenesis of the fruit fly, and acts through the
Wnt signaling pathway.
The Patched receptor protein of the
Hedgehog signaling pathway, which production acts as a
negative feedback, since the resulting increase in Patched protein on the cell surface inhibits the Hedgehog pathway.[5]