Eukaryotic cilia and flagella are specialized organelles found at the periphery of cells of diverse organisms. Intra-flagellar transport (IFT) is required for the assembly and maintenance of eukaryotic cilia and flagella, and consists of the bidirectional movement of large protein particles between the base and the distal tip of the organelle. IFT particles contain multiple copies of two distinct protein complexes, A and B, which contain at least 6 and 11 protein subunits. IFT57 is part of complex B but is not, however, required for the core subunits to stay associated. This protein is known as Huntington-interacting protein-1 in humans.