Suvarna K, Stevenson D, Meganathan R, Hudspeth M E
Department of Biological Sciences, Northern Illinois University, DeKalb, Illinois 60115, USA.
J Bacteriol. 1998 May;180(10):2782-7. doi: 10.1128/JB.180.10.2782-2787.1998.
A key reaction in the biosynthesis of menaquinone involves the conversion of the soluble bicyclic naphthalenoid compound 1, 4-dihydroxy-2-naphthoic acid (DHNA) to the membrane-bound demethylmenaquinone. The enzyme catalyzing this reaction, DHNA-octaprenyltransferase, attaches a 40-carbon side chain to DHNA. The menA gene encoding this enzyme has been cloned and localized to a 2.0-kb region of the Escherichia coli genome between cytR and glpK. DNA sequence analysis of the cloned insert revealed a 308-codon open reading frame (ORF), which by deletion analyses was shown to restore anaerobic growth of a menA mutant. Reverse-phase high-performance liquid chromatography analysis of quinones extracted from the orf-complemented cells independently confirmed the restoration of menaquinone biosynthesis, and similarly, analyses of isolated cell membranes for DHNA octaprenyltransferase activity confirmed the introduction of the menA product into the orf-complemented menA mutant. The validity of an ORF-associated putative promoter sequence was confirmed by primer extension analyses.
甲萘醌生物合成中的一个关键反应涉及可溶性双环萘类化合物1,4 - 二羟基 - 2 - 萘甲酸（DHNA）转化为膜结合的去甲基甲萘醌。催化此反应的酶，即DHNA - 辛戊烯基转移酶，将一个40碳的侧链连接到DHNA上。编码该酶的menA基因已被克隆并定位到大肠杆菌基因组中位于cytR和glpK之间的一个2.0 kb区域。对克隆插入片段的DNA序列分析揭示了一个308密码子的开放阅读框（ORF），通过缺失分析表明该开放阅读框可恢复menA突变体的厌氧生长。对从orf互补细胞中提取的醌进行反相高效液相色谱分析独立证实了甲萘醌生物合成的恢复，同样，对分离的细胞膜进行DHNA辛戊烯基转移酶活性分析证实了menA产物被引入到orf互补的menA突变体中。通过引物延伸分析证实了与ORF相关的推定启动子序列的有效性。
