Petricek M, Rutberg L, Schröder I, Hederstedt L
Department of Microbiology, University of Lund, Sweden.
J Bacteriol. 1990 May;172(5):2250-8. doi: 10.1128/jb.172.5.2250-2258.1990.
A 3.8-kilobase DNA fragment from Bacillus subtilis containing the hemA gene has been cloned and sequenced. Four open reading frames were identified. The first is hemA, encoding a protein of 50.8 kilodaltons. The primary defect of a B. subtilis 5-aminolevulinic acid-requiring mutant was identified as a cysteine-to-tyrosine substitution in the HemA protein. The predicted amino acid sequence of the B. subtilis HemA protein showed 34% identity with the Escherichia coli HemA protein, which is known to code for the NAD(P)H:glutamyl-tRNA reductase of the C5 pathway for 5-aminolevulinic acid synthesis. The B. subtilis HemA protein also complements the defect of an E. coli hemA mutant. The second open reading frame in the cloned fragment, called ORF2, codes for a protein of about 30 kilodaltons with unknown function. It is not the proposed hemB gene product porphobilinogen synthase. The third open reading frame is hemC, coding for porphobilinogen deaminase. The fourth open reading frame extends past the sequenced fragment and may be identical to hemD, coding for uroporphyrinogen III cosynthase. Analysis of deletion mutants of the hemA region suggests that (at least) hemA, ORF2, and hemC may be part of an operon.
来自枯草芽孢杆菌的一个包含hemA基因的3.8千碱基DNA片段已被克隆并测序。鉴定出了四个开放阅读框。第一个是hemA，编码一种50.8千道尔顿的蛋白质。一株需要5-氨基乙酰丙酸的枯草芽孢杆菌突变体的主要缺陷被确定为HemA蛋白中的一个半胱氨酸到酪氨酸的替换。枯草芽孢杆菌HemA蛋白的预测氨基酸序列与大肠杆菌HemA蛋白显示出34%的同一性，已知后者编码5-氨基乙酰丙酸合成C5途径的NAD(P)H:谷氨酰-tRNA还原酶。枯草芽孢杆菌HemA蛋白也能弥补大肠杆菌hemA突变体的缺陷。克隆片段中的第二个开放阅读框，称为ORF2，编码一种功能未知的约30千道尔顿的蛋白质。它不是推测的hemB基因产物胆色素原合酶。第三个开放阅读框是hemC，编码胆色素原脱氨酶。第四个开放阅读框延伸超过了测序片段，可能与编码尿卟啉原III同合酶的hemD相同。对hemA区域缺失突变体的分析表明，（至少）hemA、ORF2和hemC可能是一个操纵子的一部分。
