McNicholas P M, Javor G, Darie S, Gunsalus R P
Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90095-1489, USA.
FEMS Microbiol Lett. 1997 Jan 1;146(1):143-8. doi: 10.1111/j.1574-6968.1997.tb10184.x.
Little is known about the control of latter steps of heme biosynthesis in Escherichia coli. In this study we examined the transcriptional regulation of genes that encode two intermediate heme pathway enzymes, porphobilinogen deaminase (hemC) and uroporphyrinogen III cosynthase (hemD), and the final enzyme of the pathway, ferrochelatase (hemH). We also reexamined the regulation of hemA and the gene located immediately upstream of hemA, hemM. The regulatory regions of hemC, hemH, hemA and hemM were fused to lacZ. The resultant operon fusions were inserted into the E. coli chromosome in single copy and expression monitored under conditions of oxygen and heme limitation. Expression of hemM appeared constitutive under the conditions tested here. In contrast, expression of hemCD, hemH and hemA were shown to be mildly regulated in response to heme availability. Thus, transcription of four of the nine genes of the E. coli heme pathway appears to be only mildly regulated in response to heme limitation.
关于大肠杆菌中血红素生物合成后期步骤的调控，人们了解甚少。在本研究中，我们检测了编码两种血红素途径中间酶——胆色素原脱氨酶（hemC）和尿卟啉原III同合酶（hemD）以及该途径的终末酶——亚铁螯合酶（hemH）的基因的转录调控。我们还重新检测了hemA及其紧邻上游基因hemM的调控。将hemC、hemH、hemA和hemM的调控区域与lacZ融合。将所得的操纵子融合体单拷贝插入大肠杆菌染色体，并在氧气和血红素限制条件下监测表达情况。在此处测试的条件下，hemM的表达似乎是组成型的。相比之下，hemCD、hemH和hemA的表达显示出对血红素可用性有轻微调控。因此，大肠杆菌血红素途径九个基因中的四个基因的转录似乎仅对血红素限制有轻微调控。
