OSMOREGULATION OF GENE-EXPRESSION IN SALMONELLA-TYPHIMURIUM - PROU ENCODES AN OSMOTICALLY INDUCED BETAINE TRANSPORT-SYSTEM
OSMOREGULATION OF GENE-EXPRESSION IN SALMONELLA-TYPHIMURIUM - PROU ENCODES AN OSMOTICALLY INDUCED BETAINE TRANSPORT-SYSTEM
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DOI：
10.1128/jb.164.3.1224-1232.1985
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发表时间：
1985-01-01
影响因子：
3.2
通讯作者：
HIGGINS, CF
中科院分区：
文献类型：
--
作者：
CAIRNEY, J;BOOTH, IR;HIGGINS, CF
先前的证据表明，基因proU参与细菌细胞在高渗透压下生长的反应。使用μ-介导的lacZ操纵子融合，我们发现鼠伤寒沙门氏菌的proU基因的转录被刺激超过100倍，以响应外部渗透压的增加。我们的证据表明，膨压的变化是这些基因表达改变的原因。proU的表达独立于ompR基因，已知ompR基因参与孔蛋白表达的转录调控。因此，必须有至少两个不同的机制，外部渗透压可以影响基因表达。我们表明，处于这种渗透控制下的细胞中基因相对较少。proU基因被证明为甜菜碱保护剂编码高亲和力转运系统（Km = 1.3 μ M），甜菜碱保护剂响应渗透胁迫而积累到高浓度。即使完全导入，该转运系统也只能在高渗透压介质中发挥作用。因此，甜菜碱转运在两个水平上受渗透压调节：诱导表达和调节转运蛋白的活性。我们先前已经表明，proP基因编码低亲和力甜菜碱转运系统（J. Cairney，I. R. Booth和C. F. Higgins，J. Bacteriol.，164：1218-1223，1985）。在proP proU菌株，没有饱和的甜菜碱摄取可以检测到，虽然有一个低水平的非饱和组分在高底物浓度。因此S.鼠伤寒杆菌具有两种遗传上不同的甜菜碱摄取途径，组成性低亲和力系统（proP）和诱导性高亲和力系统（proU）。
Previous evidence has indicated that a gene, proU is involved in the response of bacterial cells to growth at high osmolarity. Using Mu-mediated lacZ operon fusions we found that transcription of the proU gene of Salmonella typhimurium is stimulated over 100-fold in response to increases in external osmolarity. Our evidence suggests that changes in turgor pressure are responsible for these alterations in gene expression. Expression of proU is independent of the ompR gene, known to be involved in osmoregulation of porin expression. Thus, there must be at least two distinct mechanism by which external osmolarity can influence gene expression. We show that there are relatively few genes in the cells which are under such osmotic control. The proU gene is shown to encode a high-affinity transport system (Km = 1.3 .mu.M) for the osmoprotectant betaine, which is accumulated to high concentrations in response to osmotic stress. Even when fully imduced, this transport system is only able to function in medium of high osmolarity. Thus, betaine transport is regulated by osmotic pressure at two levels: the induction of expression and by modulation of activity of the transport proteins. We have previously shown that the proP gene encodes a lower-affinity betaine transport system (J. Cairney, I. R. Booth, and C. F. Higgins, J. Bacteriol., 164:1218-1223, 1985). In proP proU strains, no saturable betaine uptake could be detected although there was a low-level nonsaturable component at high substrate concentrations. Thus S. typhimurium has two genetically distinct pathways for betaine uptake, a constitutive low-affinity system (proP) and an osmotically induced high-affinity system (proU).