Misra T K, Brown N L, Haberstroh L, Schmidt A, Goddette D, Silver S
Gene. 1985;34(2-3):253-62. doi: 10.1016/0378-1119(85)90134-9.
The nucleotide sequence for the 2240 bp of plasmid R100 following the merC gene of the mercuric resistance operon has been determined and compared with the homologous sequence of transposon Tn501. The sequences following merC and preceding the next structural gene merA are unrelated between R100 and Tn501 and differ in length, with 72 bp in Tn501 and 509 bp in R100. The R100 sequence has a potential open reading frame (ORF) for a 140 amino acid polypeptide with a reasonable translational start signal preceding it. The merA genes contain 1686 (Tn501) and 1695 (R100) bp respectively. When optimally aligned, the merA sequences differ in 18% of their positions. These differences were clustered in specific regions. In addition, there was one nucleotide triplet in the Tn501 sequence which has no counterpart in the R100 sequence and one dodecyl-nucleotide sequence in the R100 sequence without counterpart in Tn501. Thus the predicted merA polypeptide of Tn501 contains 561 amino acids and the R100 counterpart contains 564 amino acids. Comparison of the R100 mercuric reductase sequences with that for human glutathione reductase [Krauth-Siegel et al.: Eur. J. Biochem. 121 (1982) 259-267], for which there is a 2 A resolution electron density map [Thieme et al.: J. Mol. Biol. 152 (1981) 763-782] shows a strong homology, with 26% identical amino acids and many conservative substitutions. This homology allows the conclusion that the active site of these enzymes and the contact positions for flavin adenine dinucleotide (FAD) and NADPH are highly conserved, while the amino- and carboxyl-terminal sequences differ.
已测定汞抗性操纵子merC基因下游质粒R100的2240 bp核苷酸序列，并与转座子Tn501的同源序列进行了比较。R100和Tn501中merC下游及下一个结构基因merA之前的序列不相关且长度不同，Tn501中有72 bp，R100中有509 bp。R100序列有一个潜在的开放阅读框（ORF），编码一个140个氨基酸的多肽，其前面有一个合理的翻译起始信号。merA基因分别包含1686（Tn501）和1695（R100）bp。最佳比对时，merA序列在18%的位置上不同。这些差异集中在特定区域。此外，Tn501序列中有一个核苷酸三联体在R100序列中没有对应物，R100序列中有一个十二核苷酸序列在Tn501中没有对应物。因此，Tn501预测的merA多肽包含561个氨基酸，R100的对应多肽包含564个氨基酸。将R100汞还原酶序列与人类谷胱甘肽还原酶序列[克劳斯 - 西格尔等人：《欧洲生物化学杂志》121（1982）259 - 267]进行比较，后者有一个2 Å分辨率的电子密度图[蒂梅等人：《分子生物学杂志》152（1981）763 - 782]，结果显示出很强的同源性，有26%的氨基酸相同，还有许多保守替换。这种同源性使得可以得出结论，这些酶的活性位点以及黄素腺嘌呤二核苷酸（FAD）和NADPH的结合位置高度保守，而氨基末端和羧基末端序列不同。
