Problem: Briefly describe how cI acts as both a positive regulator and a negative regulator. Are there any other examples we have discussed where something can be both a positive and negative regulator (and if so, explain how)? Need Assignment Help?
cI can repress transcription from PL and PR by binding to OL and OR'. This will repress the lytic cycle of bacteriophage lambda. cI can also activate transcription of itself by binding to OR and activating transcription from PRM. The araC protein can also act as a positive and negative regulator. When arabinose is absent, araC is binds to araI1 and araO2 and transcription of the ara genes are repressed because the coactivator (CAP + cAMP) cannot bind to the CAP site. When arabinose is present (and there are low glucose levels), araC binds to araI1 and araI2 and allows for the coactivator to bind. This will activate transcription of the ara genes. correct if wrong or correct