Abstract
Cytoplasmic dynein is a complex containing heavy chains (HCs), intermediate chains (ICs), light intermediate chains (LICs), and light chains (LCs). The HCs are responsible for motor activity. The ICs at the tail region of the motor interact with dynactin, which is essential for dynein function. However, functions of other subunits and how they contribute to the assembly of the core complex are not clearly defined. Here, we analyzed in the filamentous fungus Aspergillus nidulans functions of the only LIC and two LCs, RobA (Roadblock/LC7) and TctexA (Tctex1) in dynein-mediated nuclear distribution (nud). Whereas the deletion mutant of tctexA did not exhibit an apparent nud mutant phenotype, the deletion mutant of robA exhibited a nud phenotype at an elevated temperature, which is similar to the previously characterized nudG (LC8) deletion mutant. Remarkably, in contrast to the single mutants, the robA and nudG double deletion mutant exhibits a severe nud phenotype at various temperatures. Thus, functions of these two LC classes overlap to some extent, but the presence of both becomes important under specific conditions. The single LIC, however, is essential for dynein function in nuclear distribution. This is evidenced by the identification of the nudN gene as the LIC coding gene, and by the nud phenotype exhibited by the LIC down-regulating mutant, alcA-LIC. Without a functional LIC, the HC-IC association is significantly weakened, and the HCs could no longer accumulate at the microtubule plus end. Thus, the LIC is essential for the assembly of the core complex of dynein in Aspergillus.
Highlights
Cytoplasmic dynein is the major minus end-directed microtubule motor in eukaryotic cells
During an effort to characterize several nud mutants whose defective gene products had not been previously identified [37], we found that the DNA fragment containing the coding region of the A. nidulans light intermediate chains (LICs) completely rescued the nud phenotype of the nudN117 mutant (Fig. 4), and further genetic analysis confirmed that it is the gene for nudN
In S. pombe, this light chains (LCs) participates in dynein function during meiosis [27, 28]
Summary
SJ002 GR5 TNO2A3 JZ11 or S-IC LZ26 LBA33 ⌬nudG/S-IC ⌬tctexA ⌬robA SL230 SL231 SL233 SL239–240 WX117 alcA-LIC WX825/S-IC JZ310–314 JZ315–317 JZ318–322 JZ323–329 ⌬robA/⌬nudG-8 ⌬tctexA/⌬nudG-22 ⌬tctexA/⌬robA-15. In S. cerevisiae, the LIC is required for dynein function in spindle orientation [36] Whereas it is implicated in offloading dynein from the microtubule-plus end to the cortex, it is clearly not required for the stability of the dynein complex [36]. Our results indicate that the Tctex homolog, TctexA, is not essential for dynein function in nuclear distribution, and the Roadblock homolog, RobA, is important for proper nuclear distribution at an elevated temperature of 42 °C, similar to the previously characterized NUDG/LC8 [25]. The robA/nudG double deletion mutant shows a severe nud phenotype at various temperatures These results suggest that the RobA and NUDG/LC8 LCs play overlapping roles in regulating dynein-mediated nuclear distribution, and the presence of both is only important at an elevated temperature.
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