It is well known that separate domains with different lipid compositions can exist in
liposomes containing mixtures of different phospholipids. The question of whether cellular
membranes contain similar lipid domains has intrigued workers for many years. One type of
domain, sphingolipid and cholesterol-based structures called membrane rafts, has received
much attention in the last few years. We will review the evidence that rafts exist in cells and
focus on their structure, or the organization of raft lipids and proteins. Our discussion of …