Doublet P, van Heijenoort J, Bohin J P, Mengin-Lecreulx D
URA 1131 du Centre National de la Recherche Scientifique (CNRS), Université Paris-Sud, Orsay, France.
J Bacteriol. 1993 May;175(10):2970-9. doi: 10.1128/jb.175.10.2970-2979.1993.
The murI gene of Escherichia coli was recently identified on the basis of its ability to complement the only mutant requiring D-glutamic acid for growth that had been described to date: strain WM335 of E. coli B/r (P. Doublet, J. van Heijenoort, and D. Mengin-Lecreulx, J. Bacteriol. 174:5772-5779, 1992). We report experiments of insertional mutagenesis of the murI gene which demonstrate that this gene is essential for the biosynthesis of D-glutamic acid, one of the specific components of cell wall peptidoglycan. A special strategy was used for the construction of strains with a disrupted copy of murI, because of a limited capability of E. coli strains grown in rich medium to internalize D-glutamic acid. The murI gene product was overproduced and identified as a glutamate racemase activity. UDP-N-acetylmuramoyl-L-alanine (UDP-MurNAc-L-Ala), which is the nucleotide substrate of the D-glutamic-acid-adding enzyme (the murD gene product) catalyzing the subsequent step in the pathway for peptidoglycan synthesis, appears to be an effector of the racemase activity.
大肠杆菌的murI基因最近是根据其能够互补迄今所描述的唯一一种生长需要D-谷氨酸的突变体而鉴定出来的：大肠杆菌B/r的WM335菌株（P. Doublet、J. van Heijenoort和D. Mengin-Lecreulx，《细菌学杂志》174:5772 - 5779，1992年）。我们报告了murI基因的插入诱变实验，这些实验表明该基因对于细胞壁肽聚糖的特定成分之一D-谷氨酸的生物合成至关重要。由于在丰富培养基中生长的大肠杆菌菌株内化D-谷氨酸的能力有限，因此采用了一种特殊策略来构建murI基因拷贝被破坏的菌株。murI基因产物被过量表达，并被鉴定为具有谷氨酸消旋酶活性。UDP-N-乙酰胞壁酰-L-丙氨酸（UDP-MurNAc-L-Ala）是催化肽聚糖合成途径后续步骤的D-谷氨酸添加酶（murD基因产物）的核苷酸底物，它似乎是消旋酶活性的一种效应物。
