Fig. 4. Endogenous ERK5 is retained in the nucleus after in situ detergent extraction. (A) HeLa cells were grown on coverslips as described before, serum-starved and stimulated with EGF (50 ng/ml, 15 minutes) or left untreated. The cells were then subjected to an in situ detergent extraction with NP-40 (Materials and Methods, 0.2%, 5 minutes). The fixed cells were stained with goat anti-ERK5 antibody (N19) and with DAPI. Phase contrast micrographs of the non-activated NP-40 untreated and treated cells demonstrates the effect of the detergent extraction. Staining with anti-histone H1 antibodies is shown as a positive control in the lower panel. (B) Rat-1 cells were grown and treated as described in A, except that the in situ NP-40 extraction used 0.5% for 10 minutes.