Abstract
The bacterial SbcC/SbcD DNA repair proteins were identified over a quarter of a century ago. Following the subsequent identification of the homologous Mre11/Rad50 complex in the eukaryotes and archaea, it has become clear that this conserved chromosomal processing machinery is central to DNA repair pathways and the maintenance of genomic stability in all forms of life. A number of experimental studies have explored this intriguing genome surveillance machinery, yielding significant insights and providing conceptual advances towards our understanding of how this complex operates to mediate DNA repair. However, the inherent complexity and dynamic nature of this chromosome-manipulating machinery continue to obfuscate experimental interrogations, and details regarding the precise mechanisms that underpin the critical repair events remain unanswered. This review will summarize our current understanding of the dramatic structural changes that occur in Mre11/Rad50 complex to mediate chromosomal tethering and accomplish the associated DNA processing events. In addition, undetermined mechanistic aspects of the DNA enzymatic pathways driven by this vital yet enigmatic chromosomal surveillance and repair apparatus will be discussed. In particular, novel and putative models of DNA damage recognition will be considered and comparisons will be made between the modes of action of the Rad50 protein and other related ATPases of the overarching SMC superfamily.
Highlights
The Mre11/Rad50 (M/R) DNA repair complex: a machinery conserved throughout evolution for the resolution of DNA double-strand breaks
Non-canonical ‘alternative’ non-homologous end-joining (NHEJ) mechanisms have been identified during which the ends of the double-strand breaks (DSBs) undergo limited processing prior to ligation and frequently the repair is thereby mediated via micro-homologies; such repair modes are referred to as micro-homology mediated endjoining (MMEJ) [6]
It is well established that the Mre11–Rad50 (M/R) complex operates during the earliest stages of DSB repair, playing critical roles in the recognition and processing of these sites of damage and influencing which of the repair mechanisms is utilized by the cell [16,17,18,19,20,21,22]
Summary
The Mre11/Rad50 (M/R) DNA repair complex: a machinery conserved throughout evolution for the resolution of DNA double-strand breaks. Recent insights into the mechanism of action of the canonical SMC family proteins, of which Rad50 is a member, may provide intriguing clues as to how the energy-dependent movement of the long coiled-coil regions could plausibly operate to organize and manipulate chromosomes [46].
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