Hirano M, Hirano T
Cold Spring Harbor Laboratory, PO Box 100, Cold Spring Harbor, NY 11724, USA.
EMBO J. 1998 Dec 1;17(23):7139-48. doi: 10.1093/emboj/17.23.7139.
SMC (structural maintenance of chromosomes) proteins are putative ATPases that are highly conserved among Bacteria, Archaea and Eucarya. Eukaryotic SMC proteins are implicated in a diverse range of chromosome dynamics including chromosome condensation, dosage compensation and recombinational repair. In eukaryotes, two different SMC proteins form a heterodimer, which in turn acts as the core component of a large protein complex. Despite recent progress, no ATP-dependent activity has been found in individual SMC subunits. We report here the first biochemical characterization of a bacterial SMC protein from Bacillus subtilis. Unlike eukaryotic versions, the B.subtilis SMC protein (BsSMC) is a simple homodimer with no associated subunits. It binds preferentially to single-stranded DNA (ssDNA) and has a ssDNA-stimulated ATPase activity. In the presence of ATP, BsSMC forms large nucleoprotein aggregates in a ssDNA-specific manner. Proteolytic cleavage of BsSMC is changed upon binding to ATP and ssDNA. The energy-dependent aggregation of ssDNA might represent a primitive type of chromosome condensation that occurs during segregation of bacterial chromosomes.
染色体结构维持（SMC）蛋白是一种假定的ATP酶，在细菌、古菌和真核生物中高度保守。真核生物的SMC蛋白参与多种染色体动态变化，包括染色体浓缩、剂量补偿和重组修复。在真核生物中，两种不同的SMC蛋白形成异源二聚体，进而作为大型蛋白质复合物的核心成分。尽管最近取得了进展，但在单个SMC亚基中尚未发现ATP依赖活性。我们在此报告了来自枯草芽孢杆菌的细菌SMC蛋白的首次生化特性。与真核生物版本不同，枯草芽孢杆菌SMC蛋白（BsSMC）是一种简单的同型二聚体，没有相关亚基。它优先结合单链DNA（ssDNA）并具有ssDNA刺激的ATP酶活性。在ATP存在下，BsSMC以ssDNA特异性方式形成大型核蛋白聚集体。BsSMC的蛋白水解切割在与ATP和ssDNA结合后发生变化。ssDNA的能量依赖性聚集可能代表细菌染色体分离过程中发生的一种原始染色体浓缩类型。
