Fig. 6. Effect of heat shock on PtK2 cells transfected with wild-type (EGPF-K5) and mutant (EGFP-K5 N176S) keratin constructs. (A,B) PtK2 cell expressing EGFP-K5 before (A) and 1 hour after (B) heat shock (15 minutes at 45°C). (C,D) PtK2 cell expressing the EGFP-K5 N176S construct, again before (C) and 1 hour after (D) heat shock. The mutant keratin incorporates well into the endogenous network (C, before heat shock). After heat shock, tiny keratin particles appear in the cell expressing the mutant keratin (D), but not in the wild-type cell (B). Again, two types of particles can be distinguished: fast moving F particles and larger slow S particles that appear to be tethered to the keratin filament network (see Movie 6).