Cytoplasmic dynein is a multi-subunit microtubule motor that uses the ATPase activity of its heavy chain to move towards the minus-end of a microtubule. In vivo, cytoplasmic dynein is important for the positioning of nuclei and spindles and the retrograde transport of vesicles, signaling molecules and viruses (Karki and Holzbaur, 1999;Schroer, 2004;Soldati and Schliwa, 2006;Greber and Way, 2006;Abe and Cavalli, 2008). Interestingly, although cytoplasmic dynein is a minus-enddirected motor, it accumulates at the microtubule plus-end in many cell types (Vaughan et al., 1999;Han et al., 2001;Ma and Chisholm, 2002;Lee et al., 2003;Sheeman et al., 2003;Lenz et al., 2006;Vogel et al., 2009). This accumulation at the microtubule plus-end is important for a variety of functions. For example, it might facilitate interaction with cortical proteins for spindle positioning Sheeman et al., 2003;Markus et al., 2009). In addition, because vesicles that need to undergo retrograde transport often start their journey at the plusend, the accumulation of dynein at the plus-end is thought to facilitate loading of membranous cargoes (Vaughan et al., 2002;Lenz et al., 2006).It has been found in several fungal organisms including Aspergillus nidulans, Saccharomyces cerevisiae and Ustilago maydis that the accumulation of dynein at the microtubule plusend depends on plus-end-directed kinesins (Zhang et al., 2003;Carvalho et al., 2004;Lenz et al., 2006;Caudron et al., 2008). In filamentous fungi and in neurons, kinesin 1 is important for plusend accumulation of dyenin (Zhang et al., 2003;Lenz et al., 2006;Yamada et al., 2009) and, importantly, as first discovered in U. maydis, dynein-mediated retrograde movement of early endosomes also depends on the function of kinesin 1 (Lenz et al., 2006;Abenza et al., 2009;Zekert and Fischer, 2009). These results strongly support the notion that plus-end accumulation of dynein is important for its function in vesicle trafficking. In filamentous fungi, the dynactin complex (Schroer, 2004) as well as several dynein subunits are also important for the accumulation of dynein at the microtubule plus-end (Zhang et al., 2002;Zhang et al., 2003;Zhang et al., 2008;Zhang et al., 2009;Liu et al., 2003;Lenz et al., 2006).Whether and how dynein activity is regulated at the plus-end remain to be addressed. It is thought that dynein must remain inactive at the plus-end until it interacts with cargo and/or other protein factors Sheeman et al., 2003;Zhang et al., 2003;Lenz et al., 2006;Steinberg, 2007). However, it is unclear whether dynein only gets activated at the plus-end or if it is already active before arriving at the plus-end. Here, we tested in A. nidulans whether dynein is an active ATPase before it arrives at the plus-end and whether plus-end localization is a prerequisite for activating the dynein ATPase. Our results suggest that dynein is an active ATPase before it arrives at the plus-end. The kinesin-1-mediated accumulation of dynein at the plus-ends might facilitate the interaction between early endosom...