The first of the Rab proteins were identified in the mid-1980s. Since then, much has been learned about the small proteins (20-25 kDa), though only about half have yet been extensively characterized. Studies suggest that the proteins and the roles they play in vesicle trafficking are quite complex. Structural analysis has shown that their association with other molecules occurs through multiple interaction surfaces. The Rab proteins are themselves linked to the cellular membrane by a lipid group joined to an amino acid. In the digital video sequences in this section, fox lung cells are shown expressing mEmerald fused to Rab11a and mCherry fused to Rab7a.