H-NS Is a Novel Transcriptional Modulator of the Ribonucleotide Reductase Genes in Escherichia coli
H-NS Is a Novel Transcriptional Modulator of the Ribonucleotide Reductase Genes in Escherichia coli
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DOI：
10.1128/jb.00490-13
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发表时间：
2013-09-01
影响因子：
3.2
通讯作者：
Torrents, Eduard
中科院分区：
文献类型：
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作者：
del Mar Cendra, Maria;Juarez, Antonio;Torrents, Eduard
核糖核苷酸还原酶（RNR）是DNA合成的必需酶，因为它们负责从其相应的核糖核苷酸产生四种脱氧核糖核苷酸（dNTP）。大肠杆菌含有两类需氧RNR，由nrdAB（Ia类）和nrdHIEF（Ib类）操纵子编码，以及第三类RNR，其在厌氧条件下起作用并由nrdDG（III类）操纵子编码。由于细胞中四种dNTPs数量的不平衡导致诱变率的增加，因此在细菌染色体复制期间必须严格调节RNR的活性和表达。这些基因的转录调控需要几种转录因子（包括DnaA，IciA，FIS [倒位刺激因子]，Fnr，Fur和NrdR），这取决于RNR类别;然而，决定某些RNR基因在不同环境条件下表达的因子尚不清楚。我们发现，H-NS调节nrdAB和nrdDG操纵子的表达。H-NS抑制需氧和厌氧生长细胞中的表达。在需氧条件下，阻遏发生在生长的指数期以及从指数期到稳定期的过渡期，此时不需要dNTPs。在缺氧条件下，阻遏主要发生在指数生长的细胞中。用来自nrdAB操纵子调控区的两个DNA片段进行的电泳迁移率测定证明了H-NS与这些序列的直接相互作用。
Ribonucleotide reductases (RNRs) are essential enzymes for DNA synthesis because they are responsible for the production of the four deoxyribonucleotides (dNTPs) from their corresponding ribonucleotides. Escherichia coli contains two classes of aerobic RNRs, encoded by the nrdAB (class Ia) and nrdHIEF (class Ib) operons, and a third RNR class, which is functional under anaerobic conditions and is encoded by the nrdDG (class III) operon. Because cellular imbalances in the amounts of the four dNTPs cause an increase in the rate of mutagenesis, the activity and the expression of RNRs must be tightly regulated during bacterial chromosome replication. The transcriptional regulation of these genes requires several transcription factors (including DnaA, IciA, FIS [factor for inversion stimulation], Fnr, Fur, and NrdR), depending on the RNR class; however, the factors that dictate the expression of some RNR genes in response to different environmental conditions are not known. We show that H-NS modulates the expression of the nrdAB and nrdDG operons. H-NS represses expression both in aerobically and in anaerobically growing cells. Under aerobic conditions, repression occurs at the exponential phase of growth as well as at the transition from the exponential to the stationary phase, a period when no dNTPs are needed. Under anoxic conditions, repression occurs mainly in exponentially growing cells. Electrophoretic mobility assays performed with two DNA fragments from the regulatory region of the nrdAB operon demonstrated the direct interaction of H-NS with these sequences.