Abstract
The human Mre11/Rad50 complex is one of the key factors in genome maintenance pathways. Previous nanoscale imaging by atomic force microscopy (AFM) showed that the ring-like structure of the human Mre11/Rad50 complex transiently opens at the zinc hook of Rad50. However, imaging of the human Mre11/Rad50 complex by high-speed AFM shows that the Rad50 coiled-coil arms are consistently bridged by the dimerized hooks while the Mre11/Rad50 ring opens by disconnecting the head domains; resembling other SMC proteins such as cohesin or condensin. These architectural features are conserved in the yeast and bacterial Mre11/Rad50 complexes. Yeast strains harboring the chimeric Mre11/Rad50 complex containing the SMC hinge of bacterial condensin MukB instead of the RAD50 hook properly functions in DNA repair. We propose that the basic role of the Rad50 hook is similar to that of the SMC hinge, which serves as rather stable dimerization interface.
Highlights
The human Mre11/Rad[50] complex is one of the key factors in genome maintenance pathways
There are two homo-dimerization sites locating both ends of the long coiled-coil arm of Rad[50], which are believed to be important for the M2R2 complex to form a ringshaped structure (Fig. 1a, “ring”)
To observe the human Mre11/Rad50/ Nbs1 (MRN) complex under a physiologically relevant condition, we directly visualized it on bare mica surface in a buffer by using HS-atomic force microscopy (AFM)
Summary
The human Mre11/Rad[50] complex is one of the key factors in genome maintenance pathways. Imaging of the human Mre11/Rad[50] complex by high-speed AFM shows that the Rad[50] coiled-coil arms are consistently bridged by the dimerized hooks while the Mre11/Rad[50] ring opens by disconnecting the head domains; resembling other SMC proteins such as cohesin or condensin. These architectural features are conserved in the yeast and bacterial Mre11/Rad[50] complexes. Rad[50] complex carries out the tasks by forming the intermolecular complex mediated by the hook opening/closing
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