Department of Biology, Biotechnical Faculty, University of Ljubljana, Večna pot 111, Slovenia.
BMC Microbiol. 2010 Nov 11;10:283. doi: 10.1186/1471-2180-10-283.
Phenotypic heterogeneity may ensure that a small fraction of a population survives environmental perturbations or may result in lysis in a subpopulation, to increase the survival of siblings. Genes involved in DNA repair and population dynamics play key roles in rapid responses to environmental conditions. In Escherichia coli the transcriptional repressor LexA controls a coordinated cellular response to DNA damage designated the SOS response. Expression of LexA regulated genes, e.g. colicin encoding genes, recA, lexA and umuDC, was examined utilizing transcription fusions with the promoterless gfp at the single cell level.
The investigated LexA regulated genes exhibited heterogeneity, as only in a small fraction of the population more intense fluorescence was observed. Unlike recA and lexA, the pore forming and nuclease colicin activity genes as well as umuDC, exhibited no basal level activity. However, in a lexA defective strain high level expression of the gene fusions was observed in the large majority of the cells. All of the investigated genes were expressed in a recA defective strain, albeit at lower levels, revealing expression in the absence of a spontaneous SOS response. In addition, the simultaneous expression of cka, encoding the pore forming colicin K, and lexA, investigated at the single cell level revealed high level expression of only cka in rare individual cells.
LexA regulated genes exhibit phenotypic heterogeneity as high level expression is observed in only a small subpopulation of cells. Heterogeneous expression is established primarily by stochastic factors and the binding affinity of LexA to SOS boxes.
表型异质性可以确保一小部分人群能够在环境扰动中存活下来，或者导致亚群裂解，从而增加兄弟姐妹的存活率。参与 DNA 修复和种群动态的基因在快速响应环境条件方面发挥着关键作用。在大肠杆菌中，转录抑制剂 LexA 控制着对 DNA 损伤的协调细胞反应，称为 SOS 反应。利用与启动子缺失的 gfp 的转录融合，在单细胞水平上研究了 LexA 调节基因的表达，例如编码 colicin 的基因、recA、lexA 和 umuDC。
研究的 LexA 调节基因表现出异质性，因为只有一小部分群体观察到更强的荧光。与 recA 和 lexA 不同，孔形成和核酸酶 colicin 活性基因以及 umuDC 没有基础水平的活性。然而，在 lexA 缺陷型菌株中，基因融合的高水平表达在绝大多数细胞中观察到。所有研究的基因在 recA 缺陷型菌株中均有表达，尽管水平较低，表明在没有自发 SOS 反应的情况下表达。此外，在单细胞水平上同时研究编码孔形成 colicin K 的 cka 和 lexA 的表达表明，仅在极少数个别细胞中观察到 cka 的高水平表达。
LexA 调节基因表现出表型异质性，因为高水平表达仅在一小部分细胞亚群中观察到。异质表达主要是由随机因素和 LexA 与 SOS 盒的结合亲和力建立的。
