ISOLATION AND CHARACTERIZATION OF MUTANT CHO CELL-LINES WITH COMPARTMENT-SPECIFIC RESISTANCE TO BREFELDIN-A

22 CHOBFY (BFY) cell lines were isolated at a frequency 2-30 x 10(-7) from mutagenized populations on the basis of their ability to grow in the presence of 1 mu g/ml brefeldin A (BFA). Four of the five mutant l ines tested are genetically stable and none of the mutant lines charac terized degrade this drug. Immunofluorescence studies reveal that wher eas early endosomes and the Golgi complex have nearly identical BFA se nsitivities in the parent CHO line, the relative sensitivities of thes e two organelles were dramatically altered in all six mutant lines tes ted. Four cell lines maintain normal Golgi appearance at a BFA concent ration as high as 10 mu g/ml. Mutant lines show wide variation in the level of resistance to growth inhibition by BFA, but none of the mutan t lines characterized grow above 2 mu g/ml BFA. This specific growth i nhibition is observed under conditions where Golgi morphology and func tion remain unaffected, suggesting that some factor(s) unrelated to Go lgi function remains sensitive to BFA in BFY mutant lines. These obser vations provide strong evidence for the presence of multiple, organell e-specific targets for BFA. Cell-free measurements with membrane extra cts establish that resistance to BFA in BFY-1 cells involves a membran e-associated factor distinct from ARFs and coatomers. This collection of mutant lines may prove valuable for the identification of intracell ular target(s) for BFA and/or of effecters that interact upstream or d ownstream with these targets, thereby uncovering the cascade which reg ulates assembly of organelle-specific coats.