Department of Plant and Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel.
Res Microbiol. 2011 Jun;162(5):461-9. doi: 10.1016/j.resmic.2011.03.005. Epub 2011 Mar 21.
The Escherichia coli yjbEFGH operon, encoding genes involved in exopolysaccharide production, has previously been shown to be induced by osmotic stress and to be negatively regulated by σ(38). Promoter analysis suggested that like most E. coli genes, its transcription is driven by the housekeeping sigma factor σ(70). Indeed, manipulation of any of the other five alternative sigma factors did not affect its induction by osmotic stress. Surprisingly, when assayed in a strain expressing low levels of σ(70), yjbEFGH induction in response to osmotic stress was higher than in a strain expressing normal levels of σ(70). Similar phenomena were observed in the σ(70)-driven promoters of sulA, uvrA, recA, fecI, entC and lacZ, the transcription of which is directly controlled by a repressor protein (LexA, Fur and LacI), but not in promoters of the housekeeping genes ftsA and ftsY, or in σ(38)-driven treA promoter. Since transcription factors are generally present in the cell in low numbers, we hypothesize that a decrease in σ(70), that drives the expression of lexA, fur and lacI as well, further diminishes their number in the cell and thus de-represses the induction of genes which are subjected to their repression.
大肠杆菌 yjbEFGH 操纵子，编码与胞外多糖产生有关的基因，先前已被证明受渗透压胁迫诱导，并受 σ(38)负调控。启动子分析表明，与大多数大肠杆菌基因一样，其转录由管家因子 σ(70)驱动。事实上，对其他五个替代 σ 因子中的任何一个进行操作，都不会影响其对渗透压胁迫的诱导。令人惊讶的是，在表达低水平 σ(70)的菌株中进行检测时，yjbEFGH 对渗透压胁迫的诱导高于在表达正常水平 σ(70)的菌株中。在 σ(70)驱动的 sulA、uvrA、recA、fecI、entC 和 lacZ 启动子中也观察到了类似的现象，这些启动子的转录直接受抑制蛋白（LexA、Fur 和 LacI）控制，但在管家基因 ftsA 和 ftsY 的启动子中或 σ(38)驱动的 treA 启动子中没有观察到这种现象。由于转录因子在细胞中的数量通常较低，我们假设 σ(70)的减少，也会进一步降低细胞中 LexA、Fur 和 LacI 的数量，从而解除对受其抑制的基因的抑制诱导。
