Ding Yan, Berezuk Alison, Khursigara Cezar M, Jarrell Ken F
Department of Biomedical and Molecular Sciences, Queen's University, KingstonON, Canada.
Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada.
Front Microbiol. 2017 Jul 17;8:1329. doi: 10.3389/fmicb.2017.01329. eCollection 2017.
In , the euryarchaeal archaellum regulator A (EarA) is required for the transcription of the operon, which is comprised of a series of genes which encode most of the proteins needed for the formation of the archaeal swimming organelle, the archaellum. In mutants deleted for (Δ), there is almost undetectable transcription of the operon, Fla proteins are not synthesized and the cells are non-archaellated. In this study, we have isolated a spontaneous mutant of a Δ mutant in which the restoration of the transcription and translation of the operon (using , the second gene of the operon, as a reporter), archaella formation and swarming motility were all restored even in the absence of EarA. Analysis of the DNA sequence from the promoter of this spontaneous mutant revealed a deletion of three adenines within a string of seven adenines in the transcription factor B recognition element (BRE). When the three adenine deletion in the BRE was regenerated in a stock culture of the Δ mutant, very similar phenotypes to that of the spontaneous mutant were observed. Deletion of the three adenines in the promoter BRE resulted in the mutant BRE having high sequence identity to BREs from promoters that have strong basal transcription level in and . These data suggest that EarA may help recruit transcription factor B to a weak BRE in the promoter of wild-type cells but is not required for transcription from the promoter with a strong BRE, as in the three adenine deletion version in the spontaneous mutant.
在嗜盐古菌中，广古菌鞭毛调节因子A（EarA）是操纵子转录所必需的，该操纵子由一系列基因组成，这些基因编码形成古菌游泳细胞器鞭毛所需的大部分蛋白质。在缺失该操纵子的突变体（Δ）中，几乎检测不到操纵子的转录，Fla蛋白不合成，细胞无鞭毛。在本研究中，我们分离出了一个Δ突变体的自发突变体，其中即使在没有EarA的情况下，操纵子的转录和翻译（使用操纵子的第二个基因作为报告基因）、鞭毛形成和群体运动性都得到了恢复。对该自发突变体操纵子启动子的DNA序列分析显示，转录因子B识别元件（BRE）中一串七个腺嘌呤内缺失了三个腺嘌呤。当在Δ突变体的原种培养物中再生BRE中的三个腺嘌呤缺失时，观察到与自发突变体非常相似的表型。操纵子启动子BRE中三个腺嘌呤的缺失导致突变的BRE与嗜盐古菌和嗜碱古菌中具有高基础转录水平的启动子的BRE具有高度序列同一性。这些数据表明，EarA可能有助于将转录因子B招募到野生型细胞操纵子启动子中的弱BRE，但对于具有强BRE的操纵子启动子的转录不是必需的，就像自发突变体中的三个腺嘌呤缺失版本一样。
