Department of Microbiology and Molecular Genetics, Institute of Medical Research Israel-Canada, The Kuvin Center for the Study of Infectious and Tropical Diseases, The Hebrew University-Hadassah Medical School, 91120, Jerusalem, Israel.
Institute of Chemistry, The Center for Nanoscience and Nanotechnology, Edmond J. Safra Campus, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
Sci Rep. 2021 Jan 15;11(1):1501. doi: 10.1038/s41598-021-81045-6.
Condensation and remodeling of nuclear genomes play an essential role in the regulation of gene expression and replication. Yet, our understanding of these processes and their regulatory role in other DNA-containing organelles, has been limited. This study focuses on the packaging of kinetoplast DNA (kDNA), the mitochondrial genome of kinetoplastids. Severe tropical diseases, affecting large human populations and livestock, are caused by pathogenic species of this group of protists. kDNA consists of several thousand DNA minicircles and several dozen DNA maxicircles that are linked topologically into a remarkable DNA network, which is condensed into a mitochondrial nucleoid. In vitro analyses implicated the replication protein UMSBP in the decondensation of kDNA, which enables the initiation of kDNA replication. Here, we monitored the condensation of kDNA, using fluorescence and atomic force microscopy. Analysis of condensation intermediates revealed that kDNA condensation proceeds via sequential hierarchical steps, where multiple interconnected local condensation foci are generated and further assemble into higher order condensation centers, leading to complete condensation of the network. This process is also affected by the maxicircles component of kDNA. The structure of condensing kDNA intermediates sheds light on the structural organization of the condensed kDNA network within the mitochondrial nucleoid.
核基因组的凝聚和重塑在基因表达和复制的调控中起着至关重要的作用。然而，我们对这些过程及其在其他含 DNA 细胞器中的调节作用的理解还很有限。本研究专注于动基体 DNA（kDNA）的包装，即动基体生物的线粒体基因组。严重的热带病影响着大量的人口和牲畜，是由该类原生动物的致病物种引起的。kDNA 由数千个 DNA 小环和几十个 DNA 大环组成，这些小环和大环在拓扑上连接成一个非凡的 DNA 网络，这个网络被凝聚成一个线粒体核仁。体外分析表明，复制蛋白 UMSBP 参与 kDNA 的去凝聚，从而启动 kDNA 的复制。在这里，我们使用荧光和原子力显微镜监测 kDNA 的凝聚。对凝聚中间产物的分析表明，kDNA 的凝聚是通过顺序的层次步骤进行的，其中多个相互连接的局部凝聚焦点被产生，并进一步组装成更高阶的凝聚中心，导致网络的完全凝聚。这个过程也受到 kDNA 大环线成分的影响。凝聚 kDNA 中间产物的结构揭示了凝聚的 kDNA 网络在线粒体核仁内的结构组织。
