Smart James L, Bauer Carl E
Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
J Bacteriol. 2006 Feb;188(4):1567-76. doi: 10.1128/JB.188.4.1567-1576.2006.
We demonstrate that the expression of hem genes in Rhodobacter capsulatus is transcriptionally repressed in response to the exogenous addition of heme. A high-copy suppressor screen for regulators of hem gene expression resulted in the identification of an LysR-type transcriptional regulator, called HbrL, that regulates hem promoters in response to the availability of heme. HbrL is shown to activate the expression of hemA and hemZ in the absence of exogenous hemin and repress hemB expression in the presence of exogenous hemin. Heterologously expressed HbrL apoprotein binds heme b and is purified with bound heme b when expressed in the presence of 5-aminolevulinic acid. Electrophoretic gel shift analysis demonstrated that HbrL binds the promoter region of hemA, hemB, and hemZ as well as its own promoter and that the presence of heme increases the binding affinity of HbrL to hemB.
我们证明,在荚膜红细菌中,血红素基因的表达会因外源添加血红素而受到转录抑制。针对血红素基因表达调控因子进行的高拷贝抑制子筛选,鉴定出一种LysR型转录调控因子,称为HbrL,它可根据血红素的可利用性来调控血红素启动子。结果表明,在没有外源血红素的情况下,HbrL可激活hemA和hemZ的表达,而在有外源血红素的情况下,HbrL会抑制hemB的表达。在5-氨基乙酰丙酸存在的情况下表达时,异源表达的HbrL脱辅基蛋白会结合血红素b,并与结合的血红素b一起纯化。电泳凝胶迁移分析表明,HbrL可结合hemA、hemB和hemZ的启动子区域以及其自身的启动子,并且血红素的存在会增加HbrL与hemB的结合亲和力。