Hansen F G, Atlung T
Department of Microbiology, Technical University of Denmark, Lyngby.
Mol Microbiol. 1995 Jan;15(1):141-8. doi: 10.1111/j.1365-2958.1995.tb02228.x.
The dnaA204 mutant, one of the so-called irreversible dnaA mutants which cannot reinitiate chromosome replication upon a shift from non-permissive to permissive growth temperature in the absence of protein synthesis, was reinvestigated using flow cytometry and marker frequency analysis. In a temperature down-shift experiment and in the presence of protein synthesis the dnaA204 mutant reinitiates chromosome replication very fast. Using a lac promoter-controlled wild type or a dnaA204 mutant gene carried on a plasmid, we have observed instantaneous initiation of replication when synthesis of DnaA protein is induced in the dnaA204 mutant at 42 degrees C. The data indicate that the dnaA204 mutant after a shift to 42 degrees C still contains functional DnaA protein, but that the activity level is below the initiation threshold. Thus, after synthesis of very small amounts of additional DnaA protein, initiation occurs very fast both after a shift to 30 degrees C, and after induction of DnaA protein synthesis at 42 degrees C. A model describing the processing of DnaA protein in mutants and in the wild type is presented.
dnaA204突变体是一种所谓的不可逆dnaA突变体，在缺乏蛋白质合成的情况下，当从非允许生长温度转变为允许生长温度时，它无法重新启动染色体复制。我们使用流式细胞术和标记频率分析对其进行了重新研究。在温度下降实验和存在蛋白质合成的情况下，dnaA204突变体能够非常快速地重新启动染色体复制。利用携带在质粒上的乳糖启动子控制的野生型或dnaA204突变体基因，我们观察到当在42℃下诱导dnaA204突变体中DnaA蛋白合成时，复制会立即启动。数据表明，转移到42℃后的dnaA204突变体仍然含有功能性DnaA蛋白，但活性水平低于启动阈值。因此，在合成极少量额外的DnaA蛋白后，无论是转移到30℃后，还是在42℃下诱导DnaA蛋白合成后，启动都非常迅速。本文提出了一个描述突变体和野生型中DnaA蛋白加工过程的模型。
