Figure 4.
Mapping genetic interactions of α-tubulin mutants.(a) Venn diagram of negative interactions identified in the SGA screens for loss of TUB1 (red; tub1Δ::TUB3) and loss of TUB3 (blue; tub3Δ::TUB1). (b) String network of negative synthetic interactions among the hits from panel a. Genes are clustered by GO terms as follows: 1–6 = depicted in panel c, 7 = protein degradation/proteosome, 8 = cell cycle progression/meiosis, 9 = cell polarity/morphogenesis, 10 = Golgi/endosome/vacuole/sorting, 11 = lipid/sterol/fatty acid biosynthesis, 12 = RNA processing, 13 = ribosome/translation, and 14 = miscellaneous/unknown function. (c) Hits in representative GO-term categories that show negative synthetic interaction with loss of TUB1 (red hashed; tub1Δ::TUB3) or TUB3 (blue hashed; tub3Δ::TUB1) specifically or both (gray). Significant enrichment marked by ***, P ≤ 0.001 with Fisher’s exact test. (d) Schematics of Kar9- and Dynein-dependent spindle positioning pathways. In the Kar9 pathway, in early mitosis, Bim1 links microtubule plus ends via Kar9 to the myosin Myo2, which transports the complex toward the bud along polarized actin cables at the cell cortex (McNally, 2013). This “sweeping” of microtubule plus ends moves the associated spindle pole close to the bud neck. In the Dynein pathway, the kinesin Kip2 in complex with Bik1 localizes Dyn1 to microtubule plus ends. Dyn1 together with dynactin (not shown) is activated by contact with Num1 on the cell cortex. Active Dyn1/dynactin “slides” microtubules along the cortex, which pulls the associated spindle pole into the bud (McNally, 2013). (e) Model of negative synthetic genetic relationship between hits from the loss of TUB1 (tub1Δ::TUB3) or loss of TUB3 (tub3Δ::TUB1) SGA screens and components of the Kar9 and Dynein pathways. If the SGA hits resulting from the loss of an isotype also display negative synthetic interactions with Dynein pathway components, it indicates that isotype may share functions with the Dynein pathway (A). Negative synthetic interactions between Kar9 pathway components and isotype SGA hits suggest that isotype and the Kar9 pathway may share functions (B). (f) Heatmaps of negative synthetic interactions between the microtubule-related genes identified in the loss of TUB3 (left; tub3Δ::TUB1) and loss of TUB1 (right; tub1Δ::TUB3) SGA screens (top row) and components of the Kar9 and Dynein pathways (left column). Each position reports the pairwise synthetic genetic interaction score between the indicated isotype screen hits and Kar9/Dynein pathway components, as previously reported (Usaj et al., 2017). Pairwise score < −0.12 (red) represents strong negative interaction (scale below heatmaps). MT, microtubule. (g) Strong negative synthetic interactions between the microtubule-related hits in the loss of TUB1 (red hashed; tub1Δ::TUB3) and loss of TUB3 (blue hashed; tub3Δ::TUB1) and Kar9 or Dynein pathway components as a percentage of total interactions possible from heatmaps in panel f.

Mapping genetic interactions of α-tubulin mutants. (a) Venn diagram of negative interactions identified in the SGA screens for loss of TUB1 (red; tub1Δ::TUB3) and loss of TUB3 (blue; tub3Δ::TUB1). (b) String network of negative synthetic interactions among the hits from panel a. Genes are clustered by GO terms as follows: 1–6 = depicted in panel c, 7 = protein degradation/proteosome, 8 = cell cycle progression/meiosis, 9 = cell polarity/morphogenesis, 10 = Golgi/endosome/vacuole/sorting, 11 = lipid/sterol/fatty acid biosynthesis, 12 = RNA processing, 13 = ribosome/translation, and 14 = miscellaneous/unknown function. (c) Hits in representative GO-term categories that show negative synthetic interaction with loss of TUB1 (red hashed; tub1Δ::TUB3) or TUB3 (blue hashed; tub3Δ::TUB1) specifically or both (gray). Significant enrichment marked by ***, P ≤ 0.001 with Fisher’s exact test. (d) Schematics of Kar9- and Dynein-dependent spindle positioning pathways. In the Kar9 pathway, in early mitosis, Bim1 links microtubule plus ends via Kar9 to the myosin Myo2, which transports the complex toward the bud along polarized actin cables at the cell cortex (McNally, 2013). This “sweeping” of microtubule plus ends moves the associated spindle pole close to the bud neck. In the Dynein pathway, the kinesin Kip2 in complex with Bik1 localizes Dyn1 to microtubule plus ends. Dyn1 together with dynactin (not shown) is activated by contact with Num1 on the cell cortex. Active Dyn1/dynactin “slides” microtubules along the cortex, which pulls the associated spindle pole into the bud (McNally, 2013). (e) Model of negative synthetic genetic relationship between hits from the loss of TUB1 (tub1Δ::TUB3) or loss of TUB3 (tub3Δ::TUB1) SGA screens and components of the Kar9 and Dynein pathways. If the SGA hits resulting from the loss of an isotype also display negative synthetic interactions with Dynein pathway components, it indicates that isotype may share functions with the Dynein pathway (A). Negative synthetic interactions between Kar9 pathway components and isotype SGA hits suggest that isotype and the Kar9 pathway may share functions (B). (f) Heatmaps of negative synthetic interactions between the microtubule-related genes identified in the loss of TUB3 (left; tub3Δ::TUB1) and loss of TUB1 (right; tub1Δ::TUB3) SGA screens (top row) and components of the Kar9 and Dynein pathways (left column). Each position reports the pairwise synthetic genetic interaction score between the indicated isotype screen hits and Kar9/Dynein pathway components, as previously reported (Usaj et al., 2017). Pairwise score < −0.12 (red) represents strong negative interaction (scale below heatmaps). MT, microtubule. (g) Strong negative synthetic interactions between the microtubule-related hits in the loss of TUB1 (red hashed; tub1Δ::TUB3) and loss of TUB3 (blue hashed; tub3Δ::TUB1) and Kar9 or Dynein pathway components as a percentage of total interactions possible from heatmaps in panel f.

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