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Abstract
Cytoplasmic dynein is a minus-end-directed microtubule motor that participates in
multiple cellular activities such as organelle transport and mitotic spindle assembly
[1]. To study the dynamic behavior of cytoplasmic dynein in the filamentous fungus
Aspergillus nidulans, we replaced the gene for the cytoplasmic dynein heavy chain,
nudA, with a gene encoding a green fluorescent protein (GFP)-tagged chimera, GFP-nudA.
The GFP-NUDA fusion protein is fully functional in vivo: strains expressing only the
GFP-tagged nudA grow as well as wild-type strains. Fluorescence microscopy showed
GFP-NUDA to be in comet-like structures that moved in the hyphae toward the growing
tip. Retrograde movement of some GFP-NUDA comets after they arrived at the tip was
also observed. These dynamics of GFP-NUDA were not observed in cells treated with
a microtubule-destabilizing drug, benomyl, suggesting they are microtubule-dependent.
The rate of GFP-NUDA tip-ward movement is similar to the rate of cytoplasmic microtubule
polymerization toward the hyphal tip, suggesting that GFP-NUDA is associated and moving
with the polymerizing ends of microtubules. A mutation in actin-related protein Arp1
of the dynactin complex abolishes the presence of these dynamic GFP-NUDA structures
near the hyphal tip, suggesting a targeting role of the dynactin complex.