Clarens M, Macario A J, Conway de Macario E
Wadsworth Center Division of Molecular Medicine, New York State, Department of Health, Albany, USA.
J Mol Biol. 1995 Jul 7;250(2):191-201. doi: 10.1006/jmbi.1995.0370.
The organization and expression of the first archeael dnaK-dnaJ gene cluster cloned and sequenced have been elucidated. The work focused on the methanogen Methanosarcina mazei strain S-6, but a survey of two other strains (JC3 and LYC) and species (Methanosarcina sp. JCV and Methanosarcina acetivorans) showed that the findings are pertinent to other mesophilic methanosarcinas as well. The organization and some expression features of the archaeal genes resemble eubacterial equivalents for which comparable sequence information is available. However, the archaeal genes also display characteristics that are distinct from those of eubacterial and eucaryotic homologs. dnaK and dnaJ are transcribed into monocistronic messages. The initiation site is the same for transcription under optimal cell-growth conditions, and under stress due to a temperature upshift. The two genes are expressed constitutively at lower levels than those observed after heat shock. The constitutive and post-heat-shock expression levels are higher for dnaK than for dnaJ. Both genes withstand heat shocks of at least one and a half hours without a decline in transcript levels. While the transcription termination signals are to some extent reminiscent of those of eubacteria, the initiation signals are not. These have archaeal characteristics, which resemble those of eukaryotes. The intergenic dnaK-dnaJ region contains inverted repeats. These have the potential to build firm stem-loops in the transcript and in single-stranded DNA.
已阐明克隆并测序的首个古菌dnaK-dnaJ基因簇的组织与表达情况。该研究聚焦于产甲烷菌马氏甲烷八叠球菌S-6菌株，但对另外两个菌株（JC3和LYC）以及其他物种（马氏甲烷八叠球菌JCV和嗜乙酸马氏甲烷八叠球菌）的调查表明，这些发现也适用于其他嗜温性马氏甲烷八叠球菌。古菌基因的组织和一些表达特征类似于有可比序列信息的真细菌对应基因。然而，古菌基因也表现出与真细菌和真核生物同源物不同的特征。dnaK和dnaJ转录成单顺反子信息。在最佳细胞生长条件下以及温度升高引起的应激状态下，转录起始位点相同。这两个基因的组成型表达水平低于热休克后观察到的水平。dnaK的组成型表达水平和热休克后表达水平高于dnaJ。两个基因都能承受至少一个半小时的热休克，转录水平不会下降。虽然转录终止信号在一定程度上让人联想到真细菌的信号，但起始信号并非如此。这些起始信号具有古菌特征，类似于真核生物的特征。dnaK-dnaJ基因间区域包含反向重复序列。这些反向重复序列有可能在转录本和单链DNA中形成稳定的茎环结构。
