(c) Labelling density of PtdIns(3) P in mammalian autophagosomal membrane (mean±s.e.m.). The experiment was repeated three times and the number of colloidal goldparticles per μm2 was measured in more than ten randomly selected images. Some labelling was observed in the EF but the majority of gold particles in the EF occurred near the EF-PF boundary (white circles; see Supplementary Fig. 6c for more examples), suggesting that many of them actually represent PtdIns(3) P in the PF. 