Septum formation is regulated by the RHO4-specific exchange factors BUD3 and RGF3 and by the landmark protein BUD4 in Neurospora crassa
Septum formation is regulated by the RHO4-specific exchange factors BUD3 and RGF3 and by the landmark protein BUD4 in Neurospora crassa
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DOI：
10.1111/j.1365-2958.2010.07093.x
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发表时间：
2010-04-01
影响因子：
3.6
通讯作者：
Seiler, Stephan
中科院分区：
文献类型：
--
作者：
Justa-Schuch, Daniela;Heilig, Yvonne;Seiler, Stephan
P>；Rho GTP酶在胞质分裂过程中有多种功能，但尚未明确。通过筛选Rho-4表型缺陷(即缺乏隔膜、生长缓慢、异常分枝和细胞质渗漏)的粗糙脉孢菌Rho鸟嘌呤核苷酸交换因子突变体，我们鉴定了两株分别在芽酵母和分裂酵母的Bud3p和Rgf3同源物中存在缺陷的菌株。通过体外实验确定这些蛋白作为RHO4特异性GEF的功能。活体显微镜显示，这两个GEF和它们的靶标GTP酶在选择隔膜位置和实际隔膜过程中作为两个独立的模块。此外，我们还确定了ANILLING相关蛋白BUD4的粗面拟青霉同源物是隔膜启动所必需的，并且它的缺陷导致了典型的RO4缺陷。在间隔启动之前，BUD4作为皮质环的定位与功能BUD3或RGF3无关。这些数据将BUD4定位在隔膜过程中两个RHO4功能的上游，并使BUD4成为参与未来隔膜部位选择的皮质标记蛋白的主要候选者。芽蛋白和RHO4蛋白在隔膜孔中的持续存在表明这些蛋白在成熟隔膜中具有额外的功能。
P>Rho GTPases have multiple, yet poorly defined functions during cytokinesis. By screening a Neurospora crassa knock-out collection for Rho guanine nucleotide exchange factor (GEF) mutants that phenocopy rho-4 defects (i.e. lack of septa, slow growth, abnormal branching and cytoplasmic leakage), we identified two strains defective in homologues of Bud3p and Rgf3 of budding and fission yeast respectively. The function of these proteins as RHO4-specific GEFs was determined by in vitro assays. In vivo microscopy suggested that the two GEFs and their target GTPase act as two independent modules during the selection of the septation site and the actual septation process. Furthermore, we determined that the N. crassa homologue of the anillinrelated protein BUD4 is required for septum initiation and that its deficiency leads to typical rho4 defects. Localization of BUD4 as a cortical ring prior to septation initiation was independent of functional BUD3 or RGF3. These data position BUD4 upstream of both RHO4 functions in the septation process and make BUD4 a prime candidate for a cortical marker protein involved in the selection of future septation sites. The persistence of both BUD proteins and of RHO4 at the septal pore suggests additional functions of these proteins at mature septa.