Ci protein
Encyclopedia
Ci protein, short for Cubitus interruptus, is a zinc finger
containing transcription factor
involved in the Hedgehog signaling pathway. In the absence of a signal to the Hedgehog signaling pathway, the Ci protein is cleaved and destroyed in proteasome
s. 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.
of unknown function, an anchoring protein that binds to microtubule
s (to keep the Ci protein out of the nucleus) and an adaptor protein. 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.
Zinc finger
Zinc fingers are small protein structural motifs that can coordinate one or more zinc ions to help stabilize their folds. They can be classified into several different structural families and typically function as interaction modules that bind DNA, RNA, proteins, or small molecules...
containing transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
involved in the Hedgehog signaling pathway. In the absence of a signal to the Hedgehog signaling pathway, the Ci protein is cleaved and destroyed in proteasome
Proteasome
Proteasomes are very large protein complexes inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks...
s. It isn't, however, completely destroyed; part of the protein survives and acts as a repressor
Repressor
In molecular genetics, a repressor is a DNA-binding protein that regulates the expression of one or more genes by binding to the operator and blocking the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes. This blocking of expression is called...
in the nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, 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 kinaseKinase
In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...
of unknown function, an anchoring protein that binds to microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
s (to keep the Ci protein out of the nucleus) and an adaptor protein. When the Hedgehog signaling pathway is turned on, the Ci proteolysis
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
is suppressed and the unprocessed CI protein enters the nucleus, where it activates the transcription of its target genes.
Target genes
- The Wingless protein in DrosophilaDrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
, which is crucial to the embryogenesis of the fruit fly, and acts through the Wnt signaling pathwayWnt signaling pathwayThe Wnt signaling pathway is a network of proteins best known for their roles in embryogenesis and cancer, but also involved in normal physiological processes in adult animals.-Discovery:...
. - The Patched receptor protein of the Hedgehog signaling pathwayHedgehog signaling pathwayIn a growing embryo, cells develop differently in the head or tail end of the embryo, the left or right, and other positions. They also form segments which develop into different body parts. The hedgehog signaling pathway gives cells information that they need to make the embryo develop properly....
, which production acts as a negative feedbackNegative feedbackNegative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
, since the resulting increase in Patched protein on the cell surface inhibits the Hedgehog pathway.