Pugsley A P, Dubreuil C
Unité de Génétique Moléculaire, Institut Pasteur, Paris, France.
Mol Microbiol. 1988 Jul;2(4):473-9. doi: 10.1111/j.1365-2958.1988.tb00053.x.
The structural gene for the Escherichia coli enzyme amylomaltase, malQ, is the second gene in the malPQ operon. The nucleotide sequence of malQ shows that the gene encodes an Mr 78360 protein close to the experimentally determined Mr of purified amylomaltase (72000-74000). The malQ initiation codon was identified by sequence analysis of clustered deletions around the 5' end of the gene. One of these deletions removed the first 5 bases from the malQ coding sequence. Strains carrying a plasmid with this truncated malQ gene under lacZ promoter control and out-of-frame with the first four codons of lacZ were Mal-. The Mal+ phenotype could be restored by inserting small, random fragments of E. coli chromosomal DNA into the unique EcoRI site. Nucleotide sequencing showed that the inserts either joined the lacZ and malQ sequences in frame, or contained a new translation start signal and coding sequence in frame with malQ. These results indicate that amylomaltase could be useful as a reporter protein in gene fusion studies.
大肠杆菌淀粉麦芽酶（amylomaltase）的结构基因malQ是malPQ操纵子中的第二个基因。malQ的核苷酸序列表明，该基因编码一种分子量为78360的蛋白质，接近纯化的淀粉麦芽酶实验测定的分子量（72000 - 74000）。通过对该基因5'端附近成簇缺失的序列分析确定了malQ起始密码子。其中一个缺失从malQ编码序列中去除了前5个碱基。携带在lacZ启动子控制下且与lacZ的前四个密码子读框不同的这种截短malQ基因的质粒的菌株为Mal-。通过将大肠杆菌染色体DNA的小随机片段插入唯一的EcoRI位点，可以恢复Mal+表型。核苷酸测序表明，插入片段要么使lacZ和malQ序列读框相连，要么包含一个新的翻译起始信号和与malQ读框相同的编码序列。这些结果表明，淀粉麦芽酶在基因融合研究中可用作报告蛋白。
