Tsui H C, Zhao G, Feng G, Leung H C, Winkler M E
Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School 77030.
Mol Microbiol. 1994 Jan;11(1):189-202. doi: 10.1111/j.1365-2958.1994.tb00300.x.
We report a molecular genetic analysis of the region immediately upstream from the Escherichia coli mutL DNA repair gene at 94.8 min. An open reading frame ending 9 bp upstream from the start of mutL corresponds to a 48 kDa polypeptide detected previously in minicells. The predicted amino acid sequence of this 48 kDa polypeptide shows homology to the major N-acetylmuramoyl-L-alanine amidase autolysin of Bacillus subtilis, a known amidase of Bacillus licheniformis, and the product of a Salmonella typhimurium gene that maps near 50 min. Insertions in this upstream gene, which we named amiB, or in mutL did not affect cell shape or viability; however, overexpression of the AmiB polypeptide caused cell lysis, hypersensitivity to osmotic shock and treatment with water, and temporary autolysis by low levels of antibiotics, which are all consistent with AmiB acting as a cell-wall hydrolase. Analysis of chromosomal transcription demonstrated that amiB forms a complex operon with mutL and two additional upstream genes. mutL transcripts also originated from an internal promoter, designated PmutL, located in amiB 312 bp upstream from the translational start of mutL. Together, these results suggest that E. coli contains a second amidase possibly involved in cell-wall hydrolysis, septation, or recycling, and that transcription of this amidase is directly linked to a gene central for DNA repair.
我们报告了对大肠杆菌mutL DNA修复基因（位于94.8分钟处）紧邻上游区域的分子遗传学分析。一个开放阅读框在mutL起始位点上游9 bp处结束，对应于先前在小细胞中检测到的一种48 kDa多肽。这种48 kDa多肽的预测氨基酸序列与枯草芽孢杆菌的主要N - 乙酰胞壁酰 - L - 丙氨酸酰胺酶自溶素、地衣芽孢杆菌一种已知的酰胺酶以及鼠伤寒沙门氏菌一个位于50分钟附近基因的产物具有同源性。在这个我们命名为amiB的上游基因或mutL中插入片段不影响细胞形状或活力；然而，AmiB多肽的过表达导致细胞裂解、对渗透压休克和水处理超敏以及对低水平抗生素产生暂时自溶，这些都与AmiB作为细胞壁水解酶的作用一致。染色体转录分析表明，amiB与mutL以及另外两个上游基因形成一个复杂的操纵子。mutL转录本也起源于一个内部启动子，命名为PmutL，位于mutL翻译起始位点上游312 bp处的amiB中。总之，这些结果表明大肠杆菌含有第二种可能参与细胞壁水解、隔膜形成或循环利用的酰胺酶，并且这种酰胺酶的转录与DNA修复核心基因直接相关。
