Lai Xiaokuang, Ingram Lonnie O
Department of Microbiology and Cell Science, IFAS, University of Florida, Gainesville, FL 32611, USA.
Microbiology (Reading). 1995 Jun;141 ( Pt 6):1443-1449. doi: 10.1099/13500872-141-6-1443.
The discovery of ptsHI operon in Bacillus stearothermophilus XL-65-6 coupled with our previous report of a cel operon (Lai & Ingram, J Bacteriol 175, 6441-6450, 1993) demonstrates that this thermophilic organism contains all of the genes required for cellobiose uptake by the phosphoenolpyruvate-dependent phosphotransferase system (PTS). Genes encoding the two general PTS proteins, HPr (ptsH) and enzyme I (ptsI), were cloned and sequenced. These form an operon which includes a third small gene (ptsT) of unknown function (encoded product M(r) 18428). Both ptsH and ptsI were expressed at high levels from a single plasmid in Escherichia coli and complemented corresponding host mutations. Although the translated sequences for these genes were similar to homologues from Gram-positive mesophiles (64-77% identity), the B. stearothermophilus gene products were unusual in having a higher predicted pI and fewer negatively charged amino acid residues. Enzyme I also contained more alanine and leucine than mesophilic counterparts. Interestingly, ptsT inhibited the growth of E. coli ptsI mutants at 37 degrees C. No such inhibition was observed during incubation at a lower temperature (30 degrees C) or in E. coli DH5 alpha, which is wild-type for ptsI. The predicted translation product from ptsT contained a high proportion of basic amino acids (27%) and had a high predicted pI (pH 11.7), properties similar to bacterial histone-like proteins, but did not exhibit homology to any sequences in the current database. Regions upstream and downstream from the ptsHI operon contain genes with homology to Bacillus subtilis ptsG and wapA (wall-associated protein), respectively.
嗜热脂肪芽孢杆菌XL-65-6中ptsHI操纵子的发现，以及我们之前关于cel操纵子的报道（Lai和Ingram，《细菌学杂志》175，6441 - 6450，1993年）表明，这种嗜热生物含有磷酸烯醇丙酮酸依赖性磷酸转移酶系统（PTS）摄取纤维二糖所需的所有基因。编码两种通用PTS蛋白HPr（ptsH）和酶I（ptsI）的基因被克隆并测序。它们形成一个操纵子，其中包括一个功能未知的第三个小基因（ptsT）（编码产物M(r) 18428）。ptsH和ptsI在大肠杆菌中均从单个质粒高水平表达，并互补相应的宿主突变。尽管这些基因的翻译序列与革兰氏阳性嗜温菌的同源物相似（同一性为64 - 77%），但嗜热脂肪芽孢杆菌的基因产物不同寻常之处在于其预测的pI较高且带负电荷的氨基酸残基较少。酶I也比嗜温对应物含有更多的丙氨酸和亮氨酸。有趣的是，ptsT在37℃时抑制大肠杆菌ptsI突变体的生长。在较低温度（30℃）孵育期间或在ptsI为野生型的大肠杆菌DH5α中未观察到这种抑制作用。ptsT的预测翻译产物含有高比例的碱性氨基酸（27%）且预测的pI较高（pH 11.7），这些特性与细菌类组蛋白相似，但与当前数据库中的任何序列均无同源性。ptsHI操纵子上下游区域分别包含与枯草芽孢杆菌ptsG和wapA（壁相关蛋白）同源的基因。
