Holliday junction resolvases mediate chloroplast nucleoid segregation
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Updated: Mar 2, 2026

Single-Molecule Förster Resonance Energy Transfer Methods for Real-Time Investigation of the Holliday Junction Resolution by GEN1
Published on: September 18, 2019
Yusuke Kobayashi1, Osami Misumi2, Masaki Odahara3
1Laboratory of Plant Molecular Genetics, Department of Botany, Kyoto University, Oiwake-cho, Kita-Shirakawa, Kyoto 606-8502, Japan.
Abstract:
Holliday junctions, four-stranded DNA structures formed during homologous recombination, are disentangled by resolvases that have been found in prokaryotes and eukaryotes but not in plant organelles. Here, we identify monokaryotic chloroplast 1 (MOC1) as a Holliday junction resolvase in chloroplasts by analyzing a green alga Chlamydomonas reinhardtii mutant defective in chloroplast nucleoid (DNA-protein complex) segregation. MOC1 is structurally similar to a bacterial Holliday junction resolvase, resistance to ultraviolet (Ruv) C, and genetically conserved among green plants. Reduced or no expression of MOC1 in Arabidopsis thaliana leads to growth defects and aberrant chloroplast nucleoid segregation. In vitro biochemical analysis and high-speed atomic force microscopic analysis revealed that A. thaliana MOC 1 (AtMOC1) binds and cleaves the core of Holliday junctions symmetrically. MOC1 may mediate chloroplast nucleoid segregation in green plants by resolving Holliday junctions.
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