Edwards Andrea L, Sangurdekar Dipen P, Jeong Kyeong S, Khodursky Arkady B, Rybenkov Valentin V
Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, United States of America.
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St Paul, Minnesota, United States of America.
PLoS One. 2013 Dec 23;8(12):e84027. doi: 10.1371/journal.pone.0084027. eCollection 2013.
MukB is a bacterial SMC (structural maintenance of chromosome) protein that regulates the global folding of the Escherichia coli chromosome by bringing distant DNA segments together. We report that moderate overproduction of MukB may lead, depending on strain and growth conditions, to transient growth arrest. In DH5α cells, overproduction of MukB or MukBEF using pBAD expression system triggered growth arrest 2.5 h after induction. The exit from growth arrest was accompanied by the loss of the overproducing plasmid and a decline in the abundance of MukBEF. The arrested cells showed a compound gene expression profile which can be characterized by the following features: (i) a broad and deep downregulation of ribosomal proteins (up to 80-fold); (ii) downregulation of groups of genes encoding enzymes involved in nucleotide metabolism, respiration, and central metabolism; (iii) upregulation of some of the genes responsive to general stress; and (iv) degradation of the patterns of spatial correlations in the transcriptional activity of the chromosome. The transcriptional state of the MukB induced arrest is most similar to stationary cells and cells recovered from stationary phase into a nutrient deprived medium, to amino acid starved cells and to the cells shifting from glucose to acetate. The mukB++ state is dissimilar from all examined transcriptional states generated by protein overexpression with the possible exception of RpoE and RpoH overexpression. Thus, the transcription profile of MukB-arrested cells can be described as a combination of responses typical for other growth-arrested cells and those for overproducers of DNA binding proteins with a particularly deep down-regulation of ribosomal genes.
MukB是一种细菌SMC（染色体结构维持）蛋白，它通过将远距离的DNA片段聚集在一起，调节大肠杆菌染色体的整体折叠。我们报告称，MukB的适度过量表达可能会根据菌株和生长条件导致短暂的生长停滞。在DH5α细胞中，使用pBAD表达系统过量表达MukB或MukBEF会在诱导后2.5小时引发生长停滞。从生长停滞中恢复伴随着过量表达质粒的丢失以及MukBEF丰度的下降。停滞的细胞呈现出一种复合基因表达谱，其特征如下：（i）核糖体蛋白广泛且深度下调（高达80倍）；（ii）编码参与核苷酸代谢、呼吸和中心代谢的酶的基因组下调；（iii）一些对一般应激有反应的基因上调；（iv）染色体转录活性的空间相关性模式降解。MukB诱导的停滞的转录状态与静止细胞、从静止期恢复到营养缺乏培养基中的细胞、氨基酸饥饿细胞以及从葡萄糖转换到乙酸盐的细胞最为相似。mukB++状态与通过蛋白质过量表达产生的所有检测到的转录状态不同，RpoE和RpoH过量表达可能除外。因此，MukB停滞细胞的转录谱可以描述为其他生长停滞细胞和DNA结合蛋白过量生产者典型反应的组合，其中核糖体基因有特别深的下调。
