The basal complex (BC) is essential for T. gondii cell division but mechanistic details are lacking. Here we report a reciprocal proximity based biotinylation approach to map the BC’s proteome. We interrogate the resulting map for spatiotemporal dynamics and function by disrupting the expression of components. This highlights four architecturally distinct BC subcomplexes, the compositions of which change dynamically in correlation with changes in BC function. We identify BCC0 as a protein undergirding BC formation in five foci that precede the same symmetry seen in the apical annuli and IMC sutures. Notably, daughter budding from BCC0 progresses bidirectionally: the apical cap in apical and the rest of the IMC in basal direction. Furthermore, the essential role of the BC in cell division is contained in BCC4 and MORN1 that form a ‘rubber band’ to sequester the basal end of the assembling daughter cytoskeleton. Finally, we assign BCC1 to the non-essential, final BC constriction step.

基底复合体 (BC) 对刚地弓形虫至关重要细胞分裂，但缺乏机械细节。在这里，我们报告了一种基于相互接近的生物素化方法来绘制 BC 的蛋白质组图。我们通过破坏组件的表达来查询时空动力学和功能的结果图。这突出了四个结构不同的 BC 子复合体，其组成随着 BC 功能的变化而动态变化。我们将 BCC0 鉴定为在五个病灶中支持 BC 形成的蛋白质，这些病灶先于在顶端环和 IMC 缝合线中看到的相同对称性。值得注意的是，来自 BCC0 的女儿出芽是双向的：顶盖在顶端，IMC 的其余部分在基底方向。此外，BC 在细胞分裂中的重要作用包含在 BCC4 和 MORN1 中，它们形成“橡皮筋”以隔离组装子细胞骨架的基端。最后，我们将 BCC1 分配给非必要的最终 BC 收缩步骤。