Figure 1.6-B. Structure and function of the cystic fibrosis transmembrane 
conductance regulator (CFTR) protein. The predicted structure is that of a 
membrane bound single chain polypeptide with (N- to C-terminal): an N- 
terminal intracytoplasmic portion, a membrane spanning domain (comprised of 
6 individual membrane spanning segments) , nucleotide binding fold 1 (NBF1) , 
a regulatory (R) region, a second membrane spanning domain (similar to the 
first), nucleotide binding fold 2 (NBF2) , and a C-terminal intracytoplasmic 
tail. Data from a variety of sources have demonstrated the CFTR protein 
functions as a Cl - channel responsive to increased levels of cAMP. Activa- 
tion of the channel requires binding of ATP to NBF1 and NBF2 , and cAMP 
activation of protein kinase A (PKA) to phosphorylate residues in the R 
domain. 
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Recombinant DNA Research, Volume 16 
