of the protein is still in the er the following lanes examine the expression of cftr u03b4f508 all extracts were treated with endoglycosidase h lane 4 is the control that is cells expressing cftr u03b4f508 in lanes 5 6 7 and 8 cells expressing cftr u03b4f508 were treated overnight i e for 16 h with 100 nm mg132 20 u03bcm kifunensine 1 u03bcm and 100 nm bortezomib respectively if one compares the intensity of staining of these lanes to lane 4 it is evident that all treatments u2014 with the exception of mg132 u2014 led to the accumulation of cftr u03b4f508 it is also evident that 100 nm bortezomib last lane on the right hand side was more effective than 1 u03bcm bortezomib adjacent lane because cftr is tagged with a fluorescent protein expression in individual cells can be monitored by fluorescence activated cell sorting facs by contrast with fluorescence microscopy where individual cells are picked facs allows to survey the entire cell population in addition facs has the advantage that it allows for reasonable sample throughput finally automation and scale up is readily possible transiently transfected hek293 cells were fixed in ethanol 24 h after transfection as mentioned above and then stained with propidium iodide to label the dna the rationale was to examine the distribution of cells in the cell cycle to see if the expression of cftr or of cftr u03b4f508 was toxic or if the compounds.