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Intraflagellar transport or IFT is a bidirectional motility along axonemal microtubules that is essential for the formation (ciliogenesis) and maintenance of most eukaryotic cilia and flagella.〔()〕 It is thought to be required to build all cilia that assemble within a membrane projection from the cell surface. ''Plasmodium falciparum'' cilia and the sperm flagella of Drosophila are examples of cilia that assemble in the cytoplasm and do not require IFT. The process of IFT involves movement of large protein complexes called IFT particles or trains from the cell body to the ciliary tip and followed by their return to the cell body. The outward or anterograde movement is powered by kinesin-2 while the inward or retrograde movement is powered by cytoplasmic dynein 2/1b. The IFT particles are composed of about 20 proteins organized in two subcomplexes called complex A and B.〔(), Cole DG, Diener DR, Himelblau AL, Beech PL, Fuster JC, Rosenbaum JL. Chlamydomonas kinesin-II-dependent intraflagellar transport (IFT): IFT particles contain proteins required for ciliary assembly in Caenorhabditis elegans sensory neurons. J Cell Biol. 1998 May 18;141(4):993-1008.〕 IFT was first reported in 1993 by graduate student Keith Kozminski while working in the lab of Dr. Joel Rosenbaum at Yale University. The process of IFT has been best characterized in the biflagellate alga ''Chlamydomonas reinhardtii'' as well as the sensory cilia of the nematode ''Caenorhabditis elegans''. It has been suggested based on localization studies that IFT proteins also function outside of cilia. == Biochemistry == IFT describes the bi-directional movement of non-membrane-bound particles along the doublet microtubules of the flagellar axoneme, between the axoneme and the plasma membrane. Studies have shown that the movement of IFT particles along the microtubule is carried out by two different microtubule-based motors; the anterograde (towards the flagellar tip) motor is heterotrimeric kinesin-2, and the retrograde (towards the cell body) motor is cytoplasmic dynein 1b. IFT particles carry axonemal subunits to the site of assembly at the tip of the axoneme; thus, IFT is necessary for axonemal growth. Therefore, since the axoneme needs a continually fresh supply of proteins, an axoneme with defective IFT machinery will slowly shrink in the absence of replacement protein subunits. In healthy flagella, IFT particles reverse direction at the tip of the axoneme, and are thought to carry used proteins, or "turnover products," back to the base of the flagellum. The IFT particles themselves consist of two sub-complexes, each made up of several individual IFT proteins. The two complexes, known as 'A' and 'B,' are separable via sucrose centrifugation (both complexes at approximately 16S, but under increased ionic strength complex B sediments more slowly, thus segregating the two complexes). The many subunits of the IFT complexes have been named according to their molecular weights: * complex A contains IFT144, IFT140, IFT139, IFT122,〔 IFT121 and IFT43 * complex B contains IFT172, IFT88, IFT81, IFT80, IFT74, IFT72, IFT57, IFT52, IFT46, IFT27, and IFT20〔 The biochemical properties and biological functions of these IFT subunits are just beginning to be elucidated, for example they interact with components of the basal body like CEP170 or proteins which are required for cilium formation like tubulin chaperone and membrane proteins. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intraflagellar transport」の詳細全文を読む スポンサード リンク
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