Oshima T, Ito K, Kabayama H, Nakamura Y
Department of Tumor Biology, University of Tokyo, Japan.
Mol Gen Genet. 1995 Jun 10;247(5):521-8. doi: 10.1007/BF00290342.
Lrp (leucine-responsive regulatory protein) is a global transcription factor of Escherichia coli and regulates, negatively or positively, many genes including lysU, which encodes lysyl-tRNA synthetase. Dominant negative mutations that derepress lysU expression were isolated in this study. These mutations affected a predicted DNA-binding domain of Lrp and mutants were defective DNA-binding domain of Lrp and mutants were defective both in activation of ilvIH expression and in repression of lysU expression. Consistent with the previous notion that lrp is autoregulated, lrp expression was derepressed by these mutations and repressed by multi-copy plasmids carrying lrp+. Moreover, we found by gene fusion and Northern blot hybridization that the "histone-like" protein, H-NS, bound specifically to a promoter segment of lrp in vitro, and the level of lrp expression increased in the hns null mutant. These results indicated that the lrp gene is not only feedback regulated by Lrp but is also controlled by H-NS protein.
Lrp（亮氨酸应答调节蛋白）是大肠杆菌的一种全局转录因子，对包括lysU（编码赖氨酰 - tRNA合成酶）在内的许多基因进行负向或正向调控。在本研究中分离出了解除lysU表达抑制的显性负性突变。这些突变影响了Lrp的一个预测DNA结合结构域，突变体在Lrp的DNA结合结构域存在缺陷，并且在ilvIH表达激活和lysU表达抑制方面均有缺陷。与之前关于lrp是自我调节的观点一致，这些突变导致lrp表达解除抑制，而携带lrp +的多拷贝质粒则使其表达受到抑制。此外，我们通过基因融合和Northern印迹杂交发现，“组蛋白样”蛋白H - NS在体外特异性结合lrp的启动子片段，并且在hns缺失突变体中lrp表达水平升高。这些结果表明，lrp基因不仅受Lrp的反馈调节，还受H - NS蛋白的控制。
