Vicente M, Gomez M J, Ayala J A
Departamento de Biología Celular y del Desarrollo, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Cell Mol Life Sci. 1998 Apr;54(4):317-24. doi: 10.1007/s000180050158.
The Escherichia coli dcw cluster contains cell division genes, such as the phylogenetically ubiquitous ftsZ, and genes involved in peptidoglycan synthesis. Transcription in the cluster proceeds in the same direction as the progress of the replication fork along the chromosome. Regulation is exerted at the transcriptional and post-transcriptional levels. The absence of transcriptional termination signals may, in principle, allow extension of the transcripts initiated at the up-stream promoter (mraZ1p) even to the furthest down-stream gene (envA). Complementation tests suggest that they extend into ftsW in the central part of the cluster. In addition, the cluster contains other promoters individually regulated by cis- and trans-acting signals. Dissociation of the expression of the ftsZ gene, located after ftsQ and A near the 3' end of the cluster, from its natural regulatory signals leads to an alteration in the physiology of cell division. The complexities observed in the regulation of gene expression in the cluster may then have an important biological role. Among them, LexA-binding SOS boxes have been found at the 5' end of the cluster, preceding promoters which direct the expression of ftsI (coding for PBP3, the penicillin-binding protein involved in septum formation). A gearbox promoter, ftsQ1p, forms part of the signals regulating the transcription of ftsQ, A and Z. It is an inversely growth-dependent mechanism driven by RNA polymerase containing sigma s, the factor involved in the expression of stationary phase-specific genes. Although the dcw cluster is conserved to a different extent in a variety of bacteria, the regulation of gene expression, the presence or absence of individual genes, and even the essentiality of some of them, show variations in the phylogenetic scale which may reflect adaptation to specific life cycles.
大肠杆菌的dcw基因簇包含细胞分裂基因，如在系统发育上普遍存在的ftsZ，以及参与肽聚糖合成的基因。该基因簇中的转录方向与复制叉沿染色体的前进方向相同。调控作用于转录和转录后水平。原则上，转录终止信号的缺失可能允许从上游启动子（mraZ1p）起始的转录本延伸至最下游的基因（envA）。互补试验表明，它们延伸至基因簇中部的ftsW。此外，该基因簇还包含其他由顺式和反式作用信号单独调控的启动子。位于基因簇3'端附近ftsQ和A之后的ftsZ基因，其表达与其天然调控信号解离，会导致细胞分裂生理学的改变。在该基因簇中观察到的基因表达调控复杂性可能具有重要的生物学作用。其中，在基因簇5'端、指导ftsI（编码PBP3，参与隔膜形成的青霉素结合蛋白）表达的启动子之前，发现了LexA结合的SOS框。一个齿轮箱启动子ftsQ1p构成了调控ftsQ、A和Z转录的信号的一部分。这是一种由含有σs的RNA聚合酶驱动的反向生长依赖性机制，σs是参与稳定期特异性基因表达的因子。尽管dcw基因簇在多种细菌中在不同程度上保守，但基因表达调控、个别基因的有无，甚至其中一些基因的必要性，在系统发育尺度上都存在差异，这可能反映了对特定生命周期的适应。
