After bleaching, clathrin returns (red) to the same sites it was at before (green).

Wu et al. (page 291) find that clathrin in the existing lattices of clathrin-coated pits can exchange. This ATP-dependent process may play a part in converting hexagonal, flat clathrin lattices to curved lattices that are a mixture of hexagons and pentagons.Although Wu et al. see no clathrin exchange in an in vitro system, the exchange is rapid after photobleaching of GFP–clathrin produced in vivo. The recovery could be a function of new clathrin coats forming at the membrane, but inhibition of endocytosis (which also inhibits formation of new clathrin coats) has no effect on the recovery of clathrin fluorescence. And clathrin coats in the bleached areas are not being replaced by clathrin coats flowing in from unbleached areas, as there is no visible gradient of recovery from the outside of the bleached area inwards, and the recovering fluorescent spots are in the same positions as were the spots before bleaching.

The protein mediating the exchange of clathrin may be Hsc70, which can form a tight complex with clathrin that can transiently rebind stripped vesicles. Confirmation of this hypothesis, and a study of possible regulation, will have to wait for future work. ▪