Jaffé A, D'Ari R
Ann Inst Pasteur Microbiol (1985). 1985 Jan-Feb;136A(1):159-64. doi: 10.1016/s0769-2609(85)80036-3.
Cell division is tightly coupled to DNA replication in Escherichia coli, as evidenced by the rarity of anucleate cells in steady state cultures. When DNA synthesis is arrested, cell division also comes to a halt and filamentous growth ensues, again with little formation of anucleate cells. To test the precise role of the SfiA division inhibitor during filamentous growth, we compared sfiA+ and sfiA- strains in their response to thymine starvation. More residual division was observed in the sfiA mutant culture, and autoradiographic analysis revealed that 13% of the final population consisted of cells of normal size containing no DNA compared to 0.9% in the thymine-starved sfiA+ culture. The SfiA division inhibitor is known to be synthesized massively during thymine starvation as part of the inducible SOS response. We conclude that it prevents aberrant division and formation of anucleate cells, thus assuring proper segregation when DNA synthesis is perturbed. The SfiC division inhibition mechanism, also associated with the SOS response, does not affect cell division during thymine starvation. On the other hand, an SOS-independent mechanism of division arrest clearly comes into play during thymine starvation of a sfiA sfiC mutant: although considerable aberrant division took place, the majority of the cells formed long filaments with 1 or 2 masses of DNA. Thus, E. coli assures proper chromosome segregation by two systems when DNA replication is perturbed: the rapid, efficient SfiA division inhibitor and a less stringent SOS-independent mechanism.
在大肠杆菌中，细胞分裂与DNA复制紧密相连，稳态培养中无核细胞的稀少就证明了这一点。当DNA合成停止时，细胞分裂也会停止，继而出现丝状生长，同样几乎不会形成无核细胞。为了测试SfiA分裂抑制剂在丝状生长过程中的精确作用，我们比较了sfiA+和sfiA-菌株对胸腺嘧啶饥饿的反应。在sfiA突变体培养物中观察到更多的残余分裂，放射自显影分析显示，最终群体中13%由不含DNA的正常大小细胞组成，而在胸腺嘧啶饥饿的sfiA+培养物中这一比例为0.9%。已知SfiA分裂抑制剂在胸腺嘧啶饥饿期间作为诱导型SOS反应的一部分大量合成。我们得出结论，它可防止异常分裂和无核细胞的形成，从而在DNA合成受到干扰时确保正确的分离。同样与SOS反应相关的SfiC分裂抑制机制在胸腺嘧啶饥饿期间不影响细胞分裂。另一方面，在sfiA sfiC突变体的胸腺嘧啶饥饿期间，一种不依赖SOS的分裂停滞机制显然发挥了作用：尽管发生了相当多的异常分裂，但大多数细胞形成了带有1或2团DNA的长丝。因此，当DNA复制受到干扰时，大肠杆菌通过两种系统确保正确的染色体分离：快速、高效的SfiA分裂抑制剂和一种不那么严格的不依赖SOS的机制。
