Poole R K, Anjum M F, Membrillo-Hernández J, Kim S O, Hughes M N, Stewart V
Division of Life Sciences, King's College London, United Kingdom.
J Bacteriol. 1996 Sep;178(18):5487-92. doi: 10.1128/jb.178.18.5487-5492.1996.
Escherichia coli possesses a soluble flavohemoglobin, with an unknown function, encoded by the hmp gene. A monolysogen containing an hmp-lacZ operon fusion was constructed to determine how the hmp promoter is regulated in response to heme ligands (O2, NO) or the presence of anaerobically utilized electron acceptors (nitrate, nitrite). Expression of the phi (hmp-lacZ)1 fusion was similar during aerobic growth in minimal medium containing glucose, glycerol, maltose, or sorbitol as a carbon source. Mutations in cya (encoding adenylate cyclase) or changes in medium pH between 5 and 9 were without effect on aerobic expression. Levels of aerobic and anaerobic expression in glucose-containing minimal media were similar; both were unaffected by an arcA mutation. Anaerobic, but not aerobic, expression of phi (hmp-lacZ)1 was stimulated three- to four-fold by an fnr mutation; an apparent Fnr-binding site is present in the hmp promoter. Iron depletion of rich broth medium by the chelator 2'2'-dipyridyl (0.1 mM) enhanced hmp expression 40-fold under anaerobic conditions, tentatively attributed to effects on Fnr. At a higher chelator concentration (0.4 mM), hmp expression was also stimulated aerobically. Anaerobic expression was stimulated 6-fold by the presence of nitrate and 25-fold by the presence of nitrite. Induction by nitrate or nitrite was unaffected by narL and/or narP mutations, demonstrating regulation of hmp by these ions via mechanisms alternative to those implicated in the regulation of other respiratory genes. Nitric oxide (10 to 20 microM) stimulated aerobic phi (hmp-lacZ)1 activity by up to 19-fold; soxS and soxR mutations only slightly reduced the NO effect. We conclude that hmp expression is negatively regulated by Fnr under anaerobic conditions and that additional regulatory mechanisms are involved in the responses to oxygen, nitrogen compounds, and iron availability. Hmp is implicated in reactions with small nitrogen compounds.
大肠杆菌拥有一种可溶的黄素血红蛋白，其功能未知，由hmp基因编码。构建了一个含有hmp - lacZ操纵子融合体的单溶原菌，以确定hmp启动子如何响应血红素配体（O2、NO）或厌氧利用的电子受体（硝酸盐、亚硝酸盐）的存在而受到调控。在以葡萄糖、甘油、麦芽糖或山梨醇作为碳源的基本培养基中需氧生长期间，phi（hmp - lacZ）1融合体的表达相似。cya（编码腺苷酸环化酶）中的突变或培养基pH在5至9之间的变化对需氧表达没有影响。含葡萄糖的基本培养基中需氧和厌氧表达水平相似；两者均不受arcA突变的影响。fnr突变使phi（hmp - lacZ）1的厌氧表达（而非需氧表达）提高了三至四倍；hmp启动子中存在一个明显的Fnr结合位点。螯合剂2'2'-联吡啶（0.1 mM）对丰富肉汤培养基进行铁耗尽处理，在厌氧条件下使hmp表达增强了40倍，初步归因于对Fnr的影响。在较高的螯合剂浓度（0.4 mM）下，hmp表达在需氧条件下也受到刺激。硝酸盐的存在使厌氧表达提高了6倍，亚硝酸盐的存在使厌氧表达提高了25倍。硝酸盐或亚硝酸盐的诱导不受narL和/或narP突变的影响，表明这些离子对hmp的调控机制不同于那些与其他呼吸基因调控相关的机制。一氧化氮（10至20 microM）使需氧phi（hmp - lacZ）1活性提高了多达19倍；soxS和soxR突变仅略微降低了NO的作用。我们得出结论，在厌氧条件下hmp表达受Fnr负调控，并且在对氧气、氮化合物和铁可用性的响应中涉及其他调控机制。Hmp与小氮化合物的反应有关。
