FIGURE 6:

The coordination between csi1p and alp7p is required for accurate chromosome segregation. (A) Maximum projection live-cell images of wild-type, csi1∆, and alp7∆ cells expressing cnp1p-GFP and sid4p-mTomato from their own promoters. Anaphase B lagging chromosomes were detected in csi1∆ and alp7∆ cells (arrows). Scale bars, 2 μm. (B–D) Graphs of the percentage of wild-type, csi1∆, and alp7∆ cells (B), wild-type, csi1∆, csi1^WT, and csi1^463IPNN cells (C), and wild-type, alp7∆, alp7p^WT, alp7p^(∆307-312), and csi1^463IPNN and alp7^(∆307-312) double-mutant cells (D) displaying anaphase B lagging chromosomes. Quantification was categorized according to the spindle length (4, 5, 6, and 7 μm, respectively). Stars indicate no anaphase B lagging chromosomes. Note that csi1^463IPNN and alp7^(∆307-312) has no additive effect on anaphase B lagging chromosomes. Cell numbers analyzed are indicated. (E) A model for bipolar spindle assembly. Csi1p serves as a linking molecule between sad1p and alp7p to recruit the alp7p-alp14p complex to the SPBs for promoting bipolar spindle formation. The N-termini of sad1p and csi1p (Hou et al., 2012) and the C-termini of alp7p and alp14p (Sato et al., 2004) bind to each other, respectively. The microtubule-binding domains lie at the N-terminus (aa 1–300) of alp7p, outside of the TACC domain (Thadani et al., 2009), and the C-terminus of alp14p, adjacent to the dual TOG domains (indicated as T; Al-Bassam et al., 2012), respectively.Csi1p recruits alp7p to the SPBs through an interaction between csi1p C-terminus (aa 461–480) and a region (aa 307–312) in the TACC domain of alp7p (indicated as the protruding circular shape).