Bradshaw Niels, Losick Richard
Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
Elife. 2015 Oct 14;4:e08145. doi: 10.7554/eLife.08145.
Formation of a division septum near a randomly chosen pole during sporulation in Bacillus subtilis creates unequal sized daughter cells with dissimilar programs of gene expression. An unanswered question is how polar septation activates a transcription factor (σ(F)) selectively in the small cell. We present evidence that the upstream regulator of σ(F), the phosphatase SpoIIE, is compartmentalized in the small cell by transfer from the polar septum to the adjacent cell pole where SpoIIE is protected from proteolysis and activated. Polar recognition, protection from proteolysis, and stimulation of phosphatase activity are linked to oligomerization of SpoIIE. This mechanism for initiating cell-specific gene expression is independent of additional sporulation proteins; vegetative cells engineered to divide near a pole sequester SpoIIE and activate σ(F) in small cells. Thus, a simple model explains how SpoIIE responds to a stochastically-generated cue to activate σ(F) at the right time and in the right place.
枯草芽孢杆菌在孢子形成过程中，在随机选择的一个极附近形成隔膜会产生大小不等且基因表达程序不同的子细胞。一个尚未解决的问题是极性隔膜如何在小细胞中选择性地激活转录因子（σ(F)）。我们提供的证据表明，σ(F)的上游调节因子磷酸酶SpoIIE通过从极性隔膜转移到相邻细胞极而在小细胞中进行区室化，在该相邻细胞极处SpoIIE受到蛋白水解保护并被激活。极性识别、蛋白水解保护以及磷酸酶活性的刺激都与SpoIIE的寡聚化有关。这种启动细胞特异性基因表达的机制独立于其他孢子形成蛋白；经过工程改造使其在极附近进行分裂的营养细胞会隔离SpoIIE并在小细胞中激活σ(F)。因此，一个简单的模型解释了SpoIIE如何响应随机产生的信号，在正确的时间和地点激活σ(F)。
