In 30% of the patients with Cystic Fibrosis the mutation responsible for the problem is not the delta 508 mutation, but a point mutation in another part of the gene. A good number of these mutations are concentrated in the regulatory domain of the protein where all the PKA phosphorylation sites are localized. Combining your knowledge of signaling cascades, regulation of ion pumps, and genetics, propose a hypothesis of how the CFTR protein function is NORMALLY turned on and off in the lung cells, starting with the signal and ending with turning on of the CFTR. List all the steps. Then explain how a mutation in the regulatory domain may result in a nonfunctional CFTR protein.