The role of Cdc42p GTPase-activating proteins in assembly of the septin ring in yeast
The role of Cdc42p GTPase-activating proteins in assembly of the septin ring in yeast
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DOI：
10.1091/mbc.e03-04-0247
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发表时间：
2003-10-01
影响因子：
3.3
通讯作者：
Bi, E
中科院分区：
文献类型：
--
作者：
Caviston, JP;Longtine, M;Bi, E
septins是一个保守的GTP-结合、促凋亡形成蛋白家族。在酿酒酵母（Saccharomyces cerevisiae）中，胞隔膜在母芽颈处形成一个环，其功能似乎主要是作为一个支架，将其他蛋白质募集到颈处，在那里它们参与胞质分裂和各种其他过程。隔蛋白环的形成依赖于Rho型GTdR Cdc 42 p，但似乎独立于肌动蛋白细胞骨架。在这项研究中，我们进一步研究了septin环的形成机制。光漂白后的漂白恢复（FRAP）实验表明，在假定的芽网站的初始septin结构是不稳定的（交换亚基自由），但它被转换成一个稳定的环作为芽出现。携带cdc 42（V36 G）等位基因或缺乏两个或所有三个已知的Cdc 42 p GTP酶激活蛋白（GAP：Bem 3 p，Rga 1 p和Rga 2 p）的突变体可以将septins募集到细胞皮质，但在形成正常的septin环时受阻或延迟，并伴有形态发生缺陷。这些表型显着增强突变体，也有缺陷的Cla 4p或Gin 4p，两个蛋白激酶以前被证明是重要的正常隔环形成。Cdc 42 p GAP在细胞周期的早期和晚期与septins共定位，并且GAP的过表达可以抑制温度敏感性septin突变体的septin组织和形态发生缺陷。两者合计，这些数据表明，成熟的隔蛋白环的形成是一个过程，包括至少两个可区分的步骤，招聘的隔蛋白蛋白的推定芽网站和他们的组装成稳定的隔蛋白环。这两个步骤似乎都依赖于Cdc 42 p，而Cdc 42 p GAP和其他已知促进正常septin环形成的蛋白质似乎在组装步骤中以部分冗余的方式起作用。此外，由于最终形成一个正常的隔蛋白环的cdc 42（V36 G）或GAP突变体总是伴随着一个开关，从一个异常伸长到一个更正常的芽形态远端的环，它似乎隔蛋白环起着直接的作用，在确定模式的芽生长。
The septins are a conserved family of GTP-binding, filament-forming proteins. In the yeast Saccharomyces cerevisiae, the septins form a ring at the mother-bud neck that appears to function primarily by serving as a scaffold for the recruitment of other proteins to the neck, where they participate in cytokinesis and a variety of other processes. Formation of the septin ring depends on the Rho-type GTPase Cdc42p but appears to be independent of the actin cytoskeleton. In this study, we investigated further the mechanisms of septin-ring formation. Fluorescence-recovery-after-photobleaching (FRAP) experiments indicated that the initial septin structure at the presumptive bud site is labile (exchanges subunits freely) but that it is converted into a stable ring as the bud emerges. Mutants carrying the cdc42(V36G) allele or lacking two or all three of the known Cdc42p GTPase-activating proteins (GAPs: Bem3p, Rga1p, and Rga2p) could recruit the septins to the cell cortex but were blocked or delayed in forming a normal septin ring and had accompanying morphogenetic defects. These phenotypes were dramatically enhanced in mutants that were also defective in Cla4p or Gin4p, two protein kinases previously shown to be important for normal septin-ring formation. The Cdc42p GAPs colocalized with the septins both early and late in the cell cycle, and overexpression of the GAPs could suppress the septin-organization and morphogenetic defects of temperature-sensitive septin mutants. Taken together, the data suggest that formation of the mature septin ring is a process that consists of at least two distinguishable steps, recruitment of the septin proteins to the presumptive bud site and their assembly into the stable septin ring. Both steps appear to depend on Cdc42p, whereas the Cdc42p GAPs and the other proteins known to promote normal septin-ring formation appear to function in a partially redundant manner in the assembly step. In addition, because the eventual formation of a normal septin ring in a cdc42(V36G) or GAP mutant was invariably accompanied by a switch from an abnormally elongated to a more normal bud morphology distal to the ring, it appears that the septin ring plays a direct role in determining the pattern of bud growth.