What is "ci protein"

n. A repressor found in λ phage (a bacteriophage that particularly infects the human digestive bacteria, ''E. coli'') which turns off genetic transcription at the phage's L and R promoters, and thus prevents multiple phages from infecting a single host.

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 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.