Subunits of the dynein complex in Saccharomyces cerevisiae. Protein domain structure shown for dynein heavy chain, Dyn1, dynein intermediate chain, Pac11, dynein light intermediate chain, Dyn3, and dynein light chain (LC8-type), Dyn2. Dyn1 domain structure determined from [Mocz and Gibbons, 2001; Reck-Peterson et al., 2006; Carter et al., 2008; Markus et al., 2009]. Pac11 domain structure from [Geiser et al., 1997]. Dyn3 domain structure from [Hughes et al., 1995]. Dyn2 domain structure from [Dick et al., 1996]. Sequence conservation is shown for each protein: percent identity and percent positive as determined from BLAST searches and ClustalW2 sequence alignments. Dyn1 sequence compared to DYNC1H1 (Homo sapiens, accession number Q14204): Tail domain (aa1-1390), linker domain (aa1393-1745), AAA1 (aa1758-1977), AAA2 (aa 2053-2216), AAA3 (aa2403-2633), AAA4 (aa2732-2932), Stalk (aa3080-3237), MTBD (aa3115-3206), AAA5 (aa3379-3597), and AAA6 (aa3825-3960). Pac11 sequence compared to Dync1li1 (Rattus norvegicus, accession number Q63100): N-term (aa1-140), Serine rich region (aa141-161), and WD40 Domain (aa384-473). Dyn3 sequence compared to Dync1li2 (Rattus norvegicus, accession number Q62698): Dynein Light Intermediate Chain (DLIC) (aa163-278). Dyn2 sequence compared to LC8 (Drosophila melanogaster, accession number NP_525075): Dynein_Light superfamily (aa4-92).

Spindle movement is powered by microtubule sliding along the cell cortex. Timelapse images of GFP-labeled microtubules. Several cytoplasmic microtubules project outward from each end of the short bipolar spindle. These microtubules explore the cytoplasm by growing and shrinking. As a microtubule end hits the cell cortex, dynein pulls the microtubule past the site of interaction, drawing the spindle forward and through the bud neck. Each image is a composite of 9 planes separated by 0.5μm; stacks were captured at 10-second intervals. Scalebar: 1μm.

Model for dynein localization and function. Dynein and its activator, dynactin, are targeted to microtubule plus ends by a complex of kinesin and CLIP-170. Retention of dynein-dynactin at the plus end requires LIS1 and NudEl, and may also involve CLIP-170. By associating processively with the plus end, microtubule growth delivers dynein-dynactin to the cortical receptor, Num1. Interaction with Num1 facilitates the docking of dynein-dynactin to the cell cortex. Activation of motor activity causes dynein to then walk toward the microtubule minus end, which pulls the attached spindle pole and proximal edge of the nuclear envelope toward the anchored motor.

Protein domains and localization of Num1. A) Domain architecture of Num1. The amino-terminal coiled-coil (CC) was identified using the secondary structure prediction program, Coils. The tandem repeat region consists of twelve repeats of 64 amino acids [Verstrepen et al., 2005]. The function of this region is not known. The PH domain was confirmed by a genome-wide analysis of PH domains in budding yeast [Yu et al., 2004]. B) The PH domain is necessary and sufficient to target Num1 to the plasma membrane. Localization of full-length Num1, a truncation that lacks the PH domain (ΔPH), and the PH domain alone. Each allele is tagged with RFP and expressed from the endogenous chromosomal locus (Moore, unpublished).