Davis M A, Radnedge L, Martin K A, Hayes F, Youngren B, Austin S J
ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Centre, Maryland 21702-1201, USA.
Mol Microbiol. 1996 Sep;21(5):1029-36. doi: 10.1046/j.1365-2958.1996.721423.x.
The P1 ParA protein is an ATPase that recognizes the parA promoter region where it acts to autoregulate the P1 parA-parB operon. The ParB protein is essential for plasmid partition and recognizes the cis-acting partition site parS. The regulatory role of ParA is also essential because a controlled level of ParB protein is critical for partition. However, we show that this regulatory activity is not the only role for ParA in partition. Efficient partition can be achieved without autoregulation as long as Par protein levels are kept within a range of low values. The properties of ParA mutants in these conditions showed that ParA is essential for some critical step in the partition process that is independent of par operon regulation. The putative nucleotide-binding site for the ParA ATPase was identified and disrupted by mutation. The resulting mutant was substantially defective for autoregulation and completely inactive for partition in a system in which the need for autoregulation is abolished. Thus, the ParA nucleotide-binding site appears to be necessary both for the repressor activity of ParA and for some essential step in the partition process itself. We propose that the nucleotide-bound form of the enzyme adopts a configuration that favours binding to the operator, but that the ATPase activity of ParA is required for some energetic step in partition of the plasmid copies to daughter cells.
P1 ParA蛋白是一种ATP酶，它能识别parA启动子区域，并在该区域发挥作用以自动调节P1 parA-parB操纵子。ParB蛋白对于质粒分配至关重要，它能识别顺式作用分配位点parS。ParA的调节作用也必不可少，因为ParB蛋白的受控水平对于分配至关重要。然而，我们发现这种调节活性并非ParA在分配过程中的唯一作用。只要Par蛋白水平保持在较低值范围内，即使没有自动调节也能实现高效分配。在这些条件下ParA突变体的特性表明，ParA对于分配过程中某个关键步骤至关重要，该步骤独立于par操纵子调节。确定了ParA ATP酶的推定核苷酸结合位点，并通过突变使其破坏。在一个消除了自动调节需求的系统中，所得突变体在自动调节方面存在严重缺陷，在分配方面完全无活性。因此，ParA核苷酸结合位点似乎对于ParA的阻遏活性以及分配过程本身的某些关键步骤都是必需的。我们提出，酶的核苷酸结合形式采用有利于与操纵基因结合的构象，但ParA的ATP酶活性对于将质粒拷贝分配到子细胞的某些能量步骤是必需的。
