CovR activation of the dipeptide permease promoter (PdppA) in group A streptococcus
CovR activation of the dipeptide permease promoter (PdppA) in group A streptococcus
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DOI：
10.1128/jb.01036-06
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发表时间：
2007-02-01
影响因子：
3.2
通讯作者：
Scott, June R.
中科院分区：
文献类型：
--
作者：
Gusa, Asiya A.;Froehlich, Barbara J.;Scott, June R.
CovR是化脓性链球菌（A组链球菌[GAS]）的双组分反应调节因子，直接或间接抑制约15%的基因组，包括编码许多毒力因子的基因和自身。转录组分析还表明，一些基因被CovR激活。我们询问CovR对这些基因之一dppA（编码二肽通透酶的操纵子中的第一个基因）的调节是直接的还是间接的。CovR的直接调节建议由5 CovR的共识结合序列（CB）附近的推定启动子的存在。在这项研究中，我们鉴定了体内合成的dppA转录物的5'末端，并表明体外dppA转录的起始是相同的。我们发现CovR在体外特异性结合dppA启动子区（PdppA），其亲和力与其结合其他CovR调节的启动子的亲和力相似。通过用GG取代TT来破坏五个CB中的任何一个，在体外抑制CovR与该位点的结合，并且在两个CB处的结合似乎是合作的。在体内，CovR转录激活不受我们可以研究的四种CB中任何一种的个体突变的影响。这表明结合位点在体内是多余的。在体外，CovR在使用纯化的GAS RNA聚合酶和线性或超螺旋DNA模板的实验中不激活PdppA的转录。因此，我们提出，在体内，CovR可能会干扰PdppA的阻遏物的结合。
CovR, the two-component response regulator of Streptococcus pyogenes (group A streptococcus [GAS]) directly or indirectly represses about 15% of the genome, including genes encoding many virulence factors and itself. Transcriptome analyses also showed that some genes are activated by CovR. We asked whether the regulation by CovR of one of these genes, dppA, the first gene in an operon encoding a dipeptide permease, is direct or indirect. Direct regulation by CovR was suggested by the presence of five CovR consensus binding sequences (CBs) near the putative promoter. In this study, we identified the 5' end of the dppA transcript synthesized in vivo and showed that the start of dppA transcription in vitro is the same. We found that CovR binds specifically to the dppA promoter region (PdppA) in vitro with an affinity similar to that at which it binds to other CovR-regulated promoters. Disruption of any of the five CBs by a substitution of GG for TT inhibited CovR binding to that site in vitro, and binding at two of the CBs appeared cooperative. In vivo, CovR activation of transcription was not affected by individual mutations of any of the four CBs that we could study. This suggests that the binding sites are redundant in vivo. In vitro, CovR did not activate transcription from PdppA in experiments using purified GAS RNA polymerase and either linear or supercoiled DNA template. Therefore, we propose that in vivo, CovR may interfere with the binding of a repressor of PdppA.