The long term objective of this work is to understand the function of the intraflagellar transport (IFT) proteins in mammals. These proteins form a complex composed of -17 polypeptides that is transported along ciliary and flagellar microtubules. IFT proteins are required for most types of ciliary assembly and are thought to function by transporting ciliary proteins from their site of synthesis in the cell body to their site of assembly in the cilium. Cilia and flagella are very prevalent in mammals and play important motility and sensory functions. The importance of these organelles is highlighted by analysis of the Tg737orpk mouse, which has a mutation in the IFT88 subunit of the IFT particle. This leads to ciliary assembly defects in many organs and causes a pleiotropic phenotype that includes blindness (retinal degeneration) and cystic kidney disease. The retinal degeneration and blindness are thought to result from an inability to properly form rod and cone outer segments in the retina. These structures, which are required to detect light in the eye, are developmentally derived from cilia. The cystic kidney disease is thought to result from defects in primary cilia, which are solitary non-motile cilia, that project from the surface of the epithelial cells that line the ducts and tubules of the nephron. These cilia are thought to be sensory organelles that play important roles in monitoring the need for cell division and controlling proliferation and differentiation. Very little is known about the functions of individual IFT particle proteins. In this proposal we will identify binding partners of IFT20, a Golgi-associated IFT particle protein. We will also address the function of IFT27, which is small G protein, in a mammalian cell culture system using shRNAs to reduce the level of the protein. Lastly, we will address the function of IFT proteins in mouse by analyzing conditional alleles of IFT genes. The work proposed here will provide new information on how cilia are assembled and how defects in these organelles cause blindness and cystic kidney disease in humans.