Verkamp E, Backman V M, Björnsson J M, Söll D, Eggertsson G
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511.
J Bacteriol. 1993 Mar;175(5):1452-6. doi: 10.1128/jb.175.5.1452-1456.1993.
In a genetic screen designed to generate Escherichia coli strains completely devoid of the heme precursor 5-aminolevulinic acid (ALA), we isolated a class of mutants which were defective for exogenous ALA uptake. The mutations, designated alu (ALA uptake), mapped to the 80-min region of the E. coli chromosome. They were complemented by a recombinant plasmid containing the dpp operon, which encodes a dipeptide permease transport system. Alu mutants displayed a severe reduction in ALA import, as did a strain with a chromosomal insertion in the first gene of the dpp operon. A recognized substrate of Dpp transport, prolyl-glycine, effectively competed with ALA for uptake. E. coli strains defective in ALA biosynthesis (hemA or hemL) require exogenous ALA to achieve wild-type growth but show limited aerobic and anaerobic growth in the absence of ALA. The presence of an alu or dpp mutation in hemA or hemL strains abolishes growth in the absence of ALA and requires increased levels of ALA for normal growth. We conclude that the alu mutations are within the dpp operon and that the dipeptide transport system mediates uptake of the important metabolite ALA.
在一项旨在构建完全缺乏血红素前体5-氨基乙酰丙酸（ALA）的大肠杆菌菌株的遗传筛选中，我们分离出了一类对外源ALA摄取存在缺陷的突变体。这些被命名为alu（ALA摄取）的突变位于大肠杆菌染色体的80分钟区域。它们可被含有dpp操纵子的重组质粒互补，该操纵子编码一种二肽通透酶转运系统。Alu突变体的ALA导入严重减少，dpp操纵子第一个基因发生染色体插入的菌株也是如此。Dpp转运的一种公认底物脯氨酰甘氨酸能有效竞争ALA的摄取。在ALA生物合成方面存在缺陷（hemA或hemL）的大肠杆菌菌株需要外源ALA才能实现野生型生长，但在没有ALA的情况下，其有氧和无氧生长都受到限制。hemA或hemL菌株中存在alu或dpp突变会导致在没有ALA的情况下无法生长，并且正常生长需要更高水平的ALA。我们得出结论，alu突变位于dpp操纵子内，并且二肽转运系统介导了重要代谢物ALA的摄取。
