Department of Biology, University of York, Wentworth Way, York YO10 5DD, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Mar 6;109(10):3754-9. doi: 10.1073/pnas.1113384109. Epub 2012 Feb 21.
Eukarya and, more recently, some bacteria have been shown to rely on a cytoskeleton-based apparatus to drive chromosome segregation. In contrast, the factors and mechanisms underpinning this fundamental process are underexplored in archaea, the third domain of life. Here we establish that the archaeon Sulfolobus solfataricus harbors a hybrid segrosome consisting of two interacting proteins, SegA and SegB, that play a key role in genome segregation in this organism. SegA is an ortholog of bacterial, Walker-type ParA proteins, whereas SegB is an archaea-specific factor lacking sequence identity to either eukaryotic or bacterial proteins, but sharing homology with a cluster of uncharacterized factors conserved in both crenarchaea and euryarchaea, the two major archaeal sub-phyla. We show that SegA is an ATPase that polymerizes in vitro and that SegB is a site-specific DNA-binding protein contacting palindromic sequences located upstream of the segAB cassette. SegB interacts with SegA in the presence of nucleotides and dramatically affects its polymerization dynamics. Our data demonstrate that SegB strongly stimulates SegA polymerization, possibly by promoting SegA nucleation and accelerating polymer growth. Increased expression levels of segAB resulted in severe growth and chromosome segregation defects, including formation of anucleate cells, compact nucleoids confined to one half of the cell compartment and fragmented nucleoids. The overall picture emerging from our findings indicates that the SegAB complex fulfills a crucial function in chromosome segregation and is the prototype of a DNA partition machine widespread across archaea.
真核生物和最近的一些细菌已被证明依赖于基于细胞骨架的装置来驱动染色体分离。相比之下，在古菌（生命的第三个领域）中，这个基本过程的基础支撑因素和机制还没有得到充分探索。在这里，我们确定了古菌 Sulfolobus solfataricus 拥有一个混合的 segrosome，由两个相互作用的蛋白质 SegA 和 SegB 组成，它们在该生物的基因组分离中发挥关键作用。SegA 是细菌 Walker 型 ParA 蛋白的同源物，而 SegB 是一种古菌特异性因子，与真核生物或细菌蛋白没有序列同一性，但与一个未被描述的因子簇具有同源性，该因子簇在 crenarchaea 和 euryarchaea 中都保守，这是两个主要的古菌亚群。我们表明 SegA 是一种 ATP 酶，可在体外聚合，而 SegB 是一种特异性的 DNA 结合蛋白，与 segAB 盒上游的回文序列结合。SegB 在核苷酸存在的情况下与 SegA 相互作用，并显著影响其聚合动力学。我们的数据表明，SegB 强烈地刺激 SegA 的聚合，可能通过促进 SegA 的成核和加速聚合物的生长。SegAB 的高表达导致严重的生长和染色体分离缺陷，包括无核细胞的形成、局限于细胞腔一半的致密核小体和片段化的核小体。我们的研究结果表明，SegAB 复合物在染色体分离中发挥着关键作用，是广泛存在于古菌中的 DNA 分区机器的原型。
