MARA LOCUS CAUSES DECREASED EXPRESSION OF OMPF PORIN IN MULTIPLE-ANTIBIOTIC-RESISTANT (MAR) MUTANTS OF ESCHERICHIA-COLI
MARA LOCUS CAUSES DECREASED EXPRESSION OF OMPF PORIN IN MULTIPLE-ANTIBIOTIC-RESISTANT (MAR) MUTANTS OF ESCHERICHIA-COLI
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DOI：
10.1128/jb.170.12.5416-5422.1988
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发表时间：
1988-12-01
影响因子：
3.2
通讯作者：
LEVY, SB
中科院分区：
文献类型：
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作者：
COHEN, SP;MCMURRY, LM;LEVY, SB
大肠杆菌的Mar（多重抗生素抗性）突变体表达染色体介导的对多种结构上不相关的亲水性和疏水性抗生素的抗性。将转座子Tn 5插入染色体上最小34.05处的marA基因座中完全逆转Mar表型（A. M.乔治和S. B。Levy，J. Bacteriol. 155：531-540，1983）。我们发现，在三月突变体的外膜的变化，孔蛋白OmpF大大减少，虽然三月突变体比细胞缺乏OmpF更耐药。来自Mar菌株而非野生型菌株的marA区域的转导导致OmpF的损失。P1将marA：：Tn 5转导到Mar突变体中部分恢复OmpF水平。因此，OmpF减少需要marA区域的突变。ompF-lacZ操纵子融合菌株的Mar突变体表达50 - 75%的β-lacZ基因。半乳糖苷酶活性的同基因非Mar亲本菌株，而蛋白融合菌株的Mar突变体表达的酶活性小于10%的非Mar菌株。这些变化被插入marA：：Tn 5完全逆转。OmpF-LacZ对渗透压和温度变化的反应性在Mar和野生型菌株中相似。虽然可能存在一些转录控制，OmpF减少似乎主要是通过转录后机制发生的。ompF mRNA的稳态水平是野生型菌株的2倍，mRNA在Mar突变体中的稳定性是野生型菌株的5倍。micF的表达，降低ompF的mRNA水平，在三月株升高，所揭示的micF-lacZ融合。删除micF基因座的菌株的研究表明，marA依赖的OmpF减少需要一个完整的micF基因座。我们的研究结果表明，marA基因座直接或间接增加micF表达，导致ompF mRNA转录后减少和OmpF量减少。
Mar (multiple antibiotic resistant) mutants of Escherichia coli express chromosomally mediated resistance to a variety of structurally unrelated hydrophilic and hydrophobic antibiotics. Insertion of transposon Tn5 into the marA locus at min 34.05 on the chromosome completely reverses the Mar phenotype (A. M. George and S. B. Levy, J. Bacteriol. 155:531-540, 1983). We found that among changes in the outer membrane of Mar mutants, porin OmpF was greatly reduced, although Mar mutants were more resistant than cells lacking only OmpF. Transduction of the marA region from a Mar strain but not a wild-type strain, led to loss of OmpF. P1 transduction of marA::Tn5 into a Mar mutant partially restored OmpF levels. Therefore, OmpF reduction required a mutation in the marA region. Mar mutants of an ompF-lacZ operon fusion strain expressed 50 to 75% of the .beta.-galactosidase activity of the isogenic non-Mar parental strain, while Mar mutants of a protein fusion strain expressed less than 10% of the enzyme activity in the non-Mar strain. These changes were completely reversed by insertion of marA::Tn5. The responsiveness of OmpF-LacZ to osmolarity and temperature changes was similar in Mar and wild-type strains. Although some transcriptional control may have been present, OmpF reduction appeared to occur primarily by a posttranscriptional mechanism. The steady-state levels of ompF mRNA were twofold lower and the mRNA was five times less stable in the Mar mutant than in the wild-type strain. Expression of micF which lowers ompF mRNA levels, was elevated in Mar strains, as revealed by a micF-lacZ fusion. Studies with strains deleted for the micF locus showed that the marA-dependent reduction of OmpF required an intact micF locus. Our findings suggest that the marA locus directly or indirectly increases micF expression, causing a posttranscriptional decrease in ompF mRNA and reduced amounts of OmpF.