An oxygen-dependent coproporphyrinogen oxidase encoded by the hemF gene of Salmonella typhimurium.
An oxygen-dependent coproporphyrinogen oxidase encoded by the hemF gene of Salmonella typhimurium.
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由鼠伤寒沙门氏菌 hemF 基因编码的氧依赖性粪卟啉原氧化酶。
DOI：
10.1128/jb.175.16.4990-4999.1993
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发表时间：
1993
影响因子：
3.2
通讯作者：
Elliott,T
中科院分区：
文献类型：
--
作者：
Xu,K;Elliott,T
鼠伤寒沙门氏菌的10步血红素生物合成途径中的第8步是副卟啉原III氧化成原卟啉IX。在遗传学研究的基础上，我们认为这一反应可能由两种不同的酶中的一种催化，一种是由hemF编码的氧依赖型酶，另一种是由hemn编码的氧非依赖型酶。在此，我们报道了鼠伤寒沙门氏菌hemF基因及其DNA序列的克隆。该蛋白的预测氨基酸序列与酵母HEM13基因编码的辅酶原氧化酶的氨基酸序列有44%的同源性。野生型鼠伤寒沙门氏菌LT-2菌株产生一种在粗提物中可检测到的氧依赖的共卟啉原氧化酶活性，这在hemF突变体中没有发现，在多拷贝质粒上携带hemF基因的菌株中过度产生。HemF基因是操纵子中的第二个基因，其上游基因的功能未知，其氨基酸序列表明与参与细胞壁合成或重塑的酰胺酶有关。上游基因与hemF由一个启动子共转录而成，该启动子通过引物延伸定位。从上游基因的omega-cm插入突变的行为中推断出较弱的hemF特异性启动子。尽管当被放置在hemF-LacZ操纵子融合的上游时，这一插入使β-半乳糖苷酶的表达减少了约7.5倍，但它仍然允许从其他野生型结构中获得足够的hemF表达，以赋予Hem+表型。HemF操纵子相对于遗传图谱是顺时针转录的。
The 8th step in the 10-step heme biosynthetic pathway of Salmonella typhimurium is the oxidation of coproporphyrinogen III to protoporphyrinogen IX. On the basis of genetic studies, we have suggested that this reaction may be catalyzed by either of two different enzymes, an oxygen-dependent one encoded by hemF or an oxygen-independent enzyme encoded by hemN. Here, we report the cloning of the S. typhimurium hemF gene and its DNA sequence. The predicted amino acid sequence of the HemF protein is 44% identical to that of the coproporphyrinogen oxidase encoded by the yeast HEM13 gene. The wild-type S. typhimurium strain LT-2 produces an oxygen-dependent coproporphyrinogen oxidase activity detectable in crude extracts, which is not found in hemF mutants and is overproduced in strains carrying the hemF gene on a multicopy plasmid. the hemF gene is the second gene in an operon with an upstream gene with an unknown function, whose amino acid sequence suggests a relation to amidases involved in cell wall synthesis or remodeling. The upstream gene and hemF are cotranscribed from a promoter which was mapped by primer extension. A weaker, hemF-specific promoter is inferred from the behavior of an omega-Cm insertion mutation in the upstream gene. Although this insertion decreases expression of beta-galactosidase about 7.5-fold when placed upstream of a hemF-lacZ operon fusion, it still allows sufficient HemF expression from an otherwise wild-type construct to confer a Hem+ phenotype. The hemF operon is transcribed clockwise with respect to the genetic map.