Circumstantial evidence has accumulated suggesting that CFTR is a regulated low-
conductance Cl-channel. To test this postulate directly, we have purified to homogeneity a
recombinant CFTR protein from a highlevel baculovirus-infected insect cell line. Evidence of
purity included one-and two-dimensional gel electrophoresis, N-terminal peptide sequence,
and quantitative amino acid analysis. Reconstitution into proteoliposomes at less than one
molecule per vesicle was accomplished by established procedures. Nystatin and ergosterol …