The organelles in a eukaryotic cell are linked by a constant flow of vesicles, budding off from one organelle and fusing with another . If unregulated, this traffic would randomise the contents of the organellar membranes. To prevent this happening, the cell has mechanisms for selecting which molecules of lipid and protein are allowed to enter the budding vesicles. The process of vesicle budding is known to involve a complex set of protein interactions, but is an important role also played by the lipid component of the membrane? An elegant new study by Roux et al.  has shown that lipids can be sorted into vesicles in the absence of any membrane proteins, suggesting that lipids are active partners in the vesicle budding process.
Lee, A.G. (2005) Lipid sorting: lipids do it on their own. Current Biology, 15 (11), 421-423. (doi:10.1016/j.cub.2005.05.030).