Department of Biology, Texas A&M University, College Station, TX 77843-3258, USA.
Protoplasma. 2012 Jul;249(3):851-6. doi: 10.1007/s00709-011-0311-4. Epub 2011 Aug 19.
Mediating the transport of flagellar precursors and removal of turnover products, intraflagellar transport (IFT) is required for flagella assembly and maintenance. The IFT apparatus is composed of the anterograde IFT motor kinesin II, the retrograde IFT motor IFT-dynein, and IFT particles containing two complexes, A and B. In order to have a balanced two-way transportation, IFT-dynein has to be carried into flagella and transported to the flagellar tip by kinesin II, where it is activated to drive the retrograde IFT back to the flagellar base. In this study, we investigated the role of complex A and complex B in the flagellar entry and exit of IFT-dynein. We showed that regardless of the amount of complex A, IFT-dynein accumulated proportionally to the amount of complex B in the flagella of fla15/ift144 and fla17-1/ift139, two complex A temperature-sensitive mutants. Complex A was depleted from both cellular and flagellar compartments in fla15/ift144 mutant. However, in fla17-1/ift139 mutant, the flagellar level of complex A was at the wild-type level, which was in radical contrast to the significantly reduced cellular amount of complex A. These results support that complex A is not required for the flagellar entry of IFT-dynein, but might be essential for the lagellar exit of IFT-dynein. Additionally, we confirmed the essential role of IFT172, a complex B subunit, in the flagellar entry of IFT-dynein. These results indicate that complexes A and B play complementary but distinct roles for IFT-dynein, with complex B carrying IFT-dynein into the flagella while complex A mediates the flagellar exit of IFT-dynein.
中介鞭毛前体的运输和周转率产物的去除，鞭毛组装和维护都需要内鞭毛运输（IFT）。IFT 仪器由正向 IFT 电机驱动蛋白 II、逆行 IFT 电机 IFT-动力蛋白和包含两个复合物 A 和 B 的 IFT 颗粒组成。为了实现平衡的双向运输，IFT-动力蛋白必须由驱动蛋白 II 携带进入鞭毛，并运输到鞭毛尖端，在那里它被激活以驱动逆行 IFT 回到鞭毛基部。在这项研究中，我们研究了复合物 A 和复合物 B 在 IFT-动力蛋白鞭毛进入和退出中的作用。我们表明，无论复合物 A 的数量如何，IFT-动力蛋白在 fla15/ift144 和 fla17-1/ift139 两种复合物 A 温度敏感突变体的鞭毛中与复合物 B 的数量成比例积累。复合物 A 从 fla15/ift144 突变体的细胞和鞭毛隔室中被耗尽。然而，在 fla17-1/ift139 突变体中，复合物 A 的鞭毛水平与野生型水平相当，这与复合物 A 的细胞数量明显减少形成鲜明对比。这些结果支持复合物 A 不是 IFT-动力蛋白进入鞭毛所必需的，但可能对 IFT-动力蛋白的鞭毛退出至关重要。此外，我们还证实了 IFT172，一种复合物 B 亚基，在 IFT-动力蛋白的鞭毛进入中起着重要作用。这些结果表明复合物 A 和 B 对 IFT-动力蛋白发挥互补但不同的作用，复合物 B 将 IFT-动力蛋白带入鞭毛，而复合物 A 介导 IFT-动力蛋白的鞭毛退出。
