Quantitative agreement has been found between observed and calculated charge mobilities through organic conductors, despite the use of many assumptions in the calculations, including: the relative strength of the intermolecular electronic coupling to the reorganization energy driving charge localization, the treatment of site variability in the material, the involvement of tunneling processes during charge hopping between sites, the use of weak-coupling-based perturbation theory to determine hopping rates, the residence times for charges on sites, the effect of the large field strengths used in experimental studies, the general appropriateness of simple one-dimensional diffusion modeling approaches, and the involvement of molecular excited states of the ions. We investigate the impact of these assumptions, concluding that all may be very significant. In some cases, methodological options are considered, and optimum procedures are determined, showing that (i) the use of Koopmans' theorem to estimate intermolecular couplings in solids is problematic and (ii) the correct expression for the residence lifetime of a charge on a crystal site. These conclusions are drawn from simulations of anisotropic charge mobilities through the β phase of mer-tris(8-hydroxyquinolinato)aluminum(III) (Alq3) crystal, a material commonly used in OLED applications. Calculations are compared that determine mobilities at finite applied field from drift velocities through either semianalytical solutions of the master equation or else kinetic Monte Carlo simulations, as well as those that determine mobilities from multidimensional diffusion coefficients at zero field by Monte Carlo and those that analytically solve simplified onedimensional diffusion models. For crystalline Alq3 itself, the calculations predict electron mobilities that are 4−6 orders of magnitude larger than those predicted by similar methods for amorphous Alq3, in agreement with experimental findings. This work vindicates recent theories describing the poor mobilities of the amorphous material, forming a complete basic picture for Alq3 conductivity.

The type I lissencephaly gene product LIS1, a key regulator of cytoplasmic dynein, is critical for cell proliferation, survival, and neuronal migration. However, little is known about the regulation of LIS1. Here, we identify a previously uncharacterized mammalian homolog of Aspergillus NudC, NudCL2 (NudC-like protein 2), as a regulator of LIS1. NudCL2 is localized to the centrosome in interphase, and spindle poles and kinetochores during mitosis, a pattern similar to the localization of LIS1 and cytoplasmic dynein. Depletion of NudCL2 destabilized LIS1 and led to phenotypes resembling those of either dynein or LIS1 deficiency. NudCL2 complexed with and enhanced the interaction between LIS1 and Hsp90. Either disruption of the LIS1-Hsp90 interaction with the C terminus of NudCL2 or inhibition of Hsp90 chaperone function by geldanamycin decreased LIS1 stability. Thus, our results suggest that NudCL2 regulates the LIS1/dynein pathway by stabilizing LIS1 with Hsp90 chaperone. This represents a hitherto undescribed mechanism of the LIS1/dynein regulation in mammalian cells.cochaperone | heat shock protein 90 | lissencephaly 1 | migration | p23

LIS1, a gene mutated in classical lissencephaly, plays essential roles in cytoplasmic dynein regulation, mitosis and cell migration. However, the regulation of LIS1 (lissencephaly protein 1) protein remains largely unknown. Genetic studies in Aspergillus nidulans have uncovered that the Nud (nuclear distribution) pathway is involved in the regulation of cytoplasmic dynein complex and a temperature-sensitive mutation in the nudC gene (L146P) greatly reduces the protein levels of NudF, an Aspergillus ortholog of LIS1. Here, we showed that L146 in Aspergillus NudC and its flanking region were highly conservative during evolution. The similar mutation in human NudC (L279P) obviously led to reduced LIS1 and cellular phenotypes similar to those of LIS1 down-regulation. To explore the underlying mechanism, we found that the p23 domain-containing protein NudC bound to the molecular chaperone Hsp90, which is also associated with LIS1. Inhibition of Hsp90 chaperone function by either geldanamycin or radicicol resulted in a decrease in LIS1 levels. Ectopic expression of Hsp90 partially reversed the degradation of LIS1 caused by overexpression of NudC-L279P. Furthermore, NudC was found to regulate the ATPase activity of Hsp90, which was repressed by the mutation of L279P. Interestingly, NudC itself was shown to possess a chaperone function, which also was suppressed by the L279P mutation. Together, these data suggest that NudC may be involved in the regulation of LIS1 stability by its chaperone function.

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Emerging data indicate that actin dynamics is associated with ciliogenesis. However, the underlying mechanism remains unclear. Here we find that nuclear distribution gene C (NudC), an Hsp90 co-chaperone, is required for actin organization and dynamics. Depletion of NudC promotes cilia elongation and increases the percentage of ciliated cells. Further results show that NudC binds to and stabilizes cofilin 1, a key regulator of actin dynamics. Knockdown of cofilin 1 also facilitates ciliogenesis. Moreover, depletion of either NudC or cofilin 1 causes similar ciliary defects in zebrafish, including curved body, pericardial edema and defective left-right asymmetry. Ectopic expression of cofilin 1 significantly reverses the phenotypes induced by NudC depletion in both cultured cells and zebrafish. Thus, our data suggest that NudC regulates actin cytoskeleton and ciliogenesis by stabilizing cofilin 1.