Control of hemA expression in Rhodobacter sphaeroides 2.4.1: regulation through alterations in the cellular redox state.
Control of hemA expression in Rhodobacter sphaeroides 2.4.1: regulation through alterations in the cellular redox state.
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球形红细菌 2.4.1 中 hemA 表达的控制：通过改变细胞氧化还原状态进行调节。
DOI：
10.1128/jb.178.4.985-993.1996
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发表时间：
1996
影响因子：
3.2
通讯作者：
Kaplan,S
中科院分区：
文献类型：
--
作者：
Zeilstra-Ryalls,JH;Kaplan,S
球形红细菌2.4.1具有合成多种四吡咯的能力，反映了这种生物体的代谢多样性，并使其能够进行有氧、厌氧、光合和重氮营养生长。hemA和hemT基因编码同工酶，催化5-氨基乙酰丙酸的形成，这是R. sphaeroides 2.4.1.作为我们研究这些基因的调控和表达的一部分，我们开发了一种遗传选择，使用转座子诱变来识别影响hemA基因有氧表达的位点。在开发这种选择中，我们发现构成紧邻hemA上游的开放阅读框的序列积极影响hemA转录。在缺乏上游开放阅读框的情况下，使用基于转座子的选择来增加hemA表达，我们分离出了三个独立的突变体。我们已经确定这些菌株中的转座子插入映射到位于1号染色体上的三个不同的基因座。其中一个转座位点定位在最近鉴定的R. sphaeroides 2.4.1厌氧调节基因fnr的同源物。通过分子标记拯救和DNA序列分析，我们发现转座位点位于R. cco操纵子的前两个基因之间。sphaeroides 2.4.1，其编码细胞色素c末端氧化酶。突变株的表型的检查显示，除了增加有氧表达的hemA，转座事件也赋予了氧不敏感的光合膜的发展。我们提出，在高氧水平存在下生长的细胞中插入转座子导致产生类似于氧还原或厌氧的细胞氧化还原状态，从而导致hemA的表达增加，以及光谱复合物形成的积累。几个模型来解释这些发现。
Rhodobacter sphaeroides 2.4.1 has the ability to synthesize a variety of tetrapyrroles, reflecting the metabolic versatility of this organism and making it capable of aerobic, anaerobic, photosynthetic, and diazotrophic growth. The hemA and hemT genes encode isozymes that catalyze the formation of 5-aminolevulinic acid, the first step in the biosynthesis of all tetrapyrroles present in R. sphaeroides 2.4.1. As part of our studies of the regulation and expression of these genes, we developed a genetic selection that uses transposon mutagenesis to identify loci affecting the aerobic expression of the hemA gene. In developing this selection, we found that sequences constituting an open reading frame immediately upstream of hemA positively affect hemA transcription. Using a transposon-based selection for increased hemA expression in the absence of the upstream open reading frame, we isolated three independent mutants. We have determined that the transposon insertions in these strains map to three different loci located on chromosome 1. One of the transposition sites mapped in the vicinity of the recently identified R. sphaeroides 2.4.1 homolog of the anaerobic regulatory gene fnr. By marker rescue and DNA sequence analysis, we found that the transposition site was located between the first two genes of the cco operon in R. sphaeroides 2.4.1, which encodes a cytochrome c terminal oxidase. Examination of the phenotype of the mutant strain revealed that, in addition to increased aerobic expression of hemA, the transposition event also conferred an oxygen-insensitive development of the photosynthetic membranes. We propose that the insertion of the transposon in cells grown in the presence of high oxygen levels has led to the generation of a cellular redox state resembling either reduced oxygen or anaerobiosis, thereby resulting in increased expression of hemA, as well as the accumulation of spectral complex formation. Several models are presented to explain these findings.