Sasarman A, Letowski J, Czaika G, Ramirez V, Nead M A, Jacobs J M, Morais R
Department of Microbiology and Immunology, Université de Montréal, QC, Canada.
Can J Microbiol. 1993 Dec;39(12):1155-61. doi: 10.1139/m93-174.
The hemG gene of Escherichia coli K12 is involved in the activity of protoporphyrinogen oxidase, the enzyme responsible for the conversion of protoporphyrinogen IX into protoporphyrin IX during heme and chlorophyll biosynthesis. The gene is located at min 87 on the genetic map of E. coli K12. The hemG gene was isolated by a mini-Mu in vivo cloning procedure. As expected, the hemG gene is able to restore normal growth to the hemG mutant, and the transformed cells display strong protoporphyrinogen oxidase activity. Sequencing of the hemG gene allowed us to identify an open reading frame of 546 nucleotides (181 amino acids), within the minimal fragment able to complement the mutant. The presumed molecular mass of the HemG protein is 21,202 Da, in agreement with values found by SDS-PAGE, in a DNA-directed coupled transcription-translation system. The identity of the first 18 amino acids at the amino-terminal end of the protein was confirmed by microsequencing. To our knowledge, this is the first cloning of a gene involved in the protoporphyrinogen oxidase activity of E. coli.
大肠杆菌K12的hemG基因参与原卟啉原氧化酶的活性，该酶在血红素和叶绿素生物合成过程中负责将原卟啉原IX转化为原卟啉IX。该基因位于大肠杆菌K12遗传图谱的87分钟处。hemG基因是通过体内微型Mu克隆程序分离得到的。正如预期的那样，hemG基因能够使hemG突变体恢复正常生长，并且转化后的细胞显示出很强的原卟啉原氧化酶活性。对hemG基因进行测序使我们能够在能够互补突变体的最小片段内鉴定出一个546个核苷酸（181个氨基酸）的开放阅读框。在DNA指导的偶联转录-翻译系统中，HemG蛋白的推测分子量为21,202 Da，与SDS-PAGE测得的值一致。通过微量测序证实了该蛋白氨基末端前18个氨基酸的序列。据我们所知，这是首次克隆参与大肠杆菌原卟啉原氧化酶活性的基因。
