Sonnenfield J M, Burns C M, Higgins C F, Hinton J C
Nuffield Department of Clinical Biochemistry, Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK.
Biochimie. 2001 Feb;83(2):243-9. doi: 10.1016/s0300-9084(01)01232-9.
The StpA protein is closely related to H-NS, the well-characterised global regulator of gene expression which is a major component of eubacterial chromatin. Despite sharing a very high degree of sequence identify and having biochemical properties in common with H-NS, the physiological function of StpA remains unknown. We show that StpA exhibits similar DNA-binding activities to H-NS. Although both display a strong preference for binding to curved DNA, StpA binds DNA with a four-fold higher affinity than H-NS, with K(d)s of 0.7 microM and 2.8 microM, respectively. It has previously been reported that expression of stpA is derepressed in an hns mutant. We have quantified the amount of StpA protein produced under this condition and find it to be only one-tenth the level of H-NS protein in wild-type cells. Our findings explain why the presence of StpA does not compensate for the lack of H-NS in an hns mutant, and why the characteristic pleiotropic hns mutant phenotype is observed.
StpA蛋白与H-NS密切相关，H-NS是一种已被充分表征的基因表达全局调节因子，是真细菌染色质的主要成分。尽管StpA与H-NS具有非常高的序列同一性，并且具有与H-NS相同的生化特性，但其生理功能仍然未知。我们发现StpA表现出与H-NS相似的DNA结合活性。虽然两者都对弯曲DNA的结合表现出强烈偏好，但StpA与DNA结合的亲和力比H-NS高四倍，解离常数（K(d)）分别为0.7微摩尔和2.8微摩尔。此前有报道称，在hns突变体中stpA的表达不受抑制。我们已经对在这种条件下产生的StpA蛋白量进行了定量，发现其仅为野生型细胞中H-NS蛋白水平的十分之一。我们的研究结果解释了为什么StpA的存在不能弥补hns突变体中H-NS的缺失，以及为什么会观察到典型的多效性hns突变体表型。
