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.
Bibliographical noteFunding Information:
This work was supported, in parts, by the United States-Israel Binational Science Foundation, Jerusalem, Israel (grants number 2011156), the Israel Science Foundation (grants number 1127/10 and 1021/14) and the Minerva Center for Bio-Hybrid complex systems. D.P. thanks the Etta and Paul Schankerman Chair of Molecular Biomedicine. We thank Dr. Dan S. Ray for the generous gift of KAPs expression vectors and antibodies, and Roman Zhuravel, for his guidance and help with the AFM analyses.
© 2021, The Author(s).