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The cystic fibrosis gene product, CFTR, is a multidomain, polytopic plasma membrane protein that belongs to the ATP-Binding Cassette transporter family. The chloride channel activity of CFTR is indispensable for normal transcellular salt and water transport in numerous organs (e.g. gastrointestinal tract, pancreas and sweat duct) and for the homeostasis of airway surface liquid layer. Our long-term goal is to elucidate the molecular and cellular basis of cystic fibrosis, one of the most prevalent genetic diseases in the Caucasian population, caused by mutations interfering with the folding, stability, activity and/or membrane trafficking of the channel. To achieve this goal, we utilize a combination of biochemical, biophysical, cell biological and genetic techniques. Another aspect of our inquiries is to gain insights into the recognition and elimination mechanism of non-native membrane proteins from post-ER/Golgi compartments in mammalian cells. The peripheral quality control of integral membrane proteins likely represents a fundamental protective mechanism against the accumulation of aggregation prone and toxic polypeptides that are generated by cellular stresses or mutations. Using conditionally misfolded model proteins, we aim at identifying the machinery responsible for the disposal of non-native plasma membrane proteins. The structural and biochemical basis of ubiquitin recognition as an endocytic and postendocytic sorting signal is also investigated.