Northern blot analysis of CFTR transcripts and immunoprecipitation. (a) Northern analysis of RNA obtained from non transfected (NT) FRT cells and from cells stably transfected with G551D-CFTR (clones A1 and 6E) or with wt-CFTR (clones N8 and N10) CFTR. Size markers are indicated at the right. The exposure time, chosen to avoid saturation, does not allow to see a clear CFTR signal from the wild type N10 clone. Nevertheless, with longer exposure time the signal was evident (see lane wtN10*). A densitometric analysis for each band is shown below corresponding lanes (A.U. are arbitrary units). After background subtraction, CFTR and G3PDH signals were fitted with gaussian functions. (b) Immunoprecipitation of G551D- and wt-CFTR proteins was done using a monoclonal antibody that recognises the C-terminus of CFTR. Fully glycosylated (band C, 175 kDa) and core glycosylated (band B, 150 kDa) CFTR can be observed in wild type and G551D clones, but not in non-transfected FRT cells (lane NT). Molecular weight standards are indicated at left. Lane N10* was obtained by loading 10 fold more protein than in the other lanes to show that a clear C band could be obtained also from the low-expression clone.