Nature 443, 569-573 (4 October 2006) | doi:10.1038/nature05160; Received 24 May 2006; Accepted 9 August 2006; Published online 27 September 2006
Reassembly of shattered chromosomes in Deinococcus radiodurans
- Université de Paris-Descartes, Faculté de Médecine, INSERM Site Necker, U571, 156 rue de Vaugirard, 75015 Paris, France
- Division of Molecular Biology, Ruder Boskovic Institute, PO Box 180, 10002 Zagreb, Croatia
- Institut de Génétique et Microbiologie, CNRS UMR8621, CEA LRC42V, Bâtiment 409, Université Paris-Sud, 91405 Orsay Cedex, France
- Institut Curie, Section Recherche, UMR 2027 CNRS, Centre Universitaire de Paris-Sud, Bâtiment 110, 91405 Orsay Cedex, France
- Mediterranean Institute for Life Sciences, Mestrovicevo setaliste bb, 21000 Split, Croatia
Dehydration or desiccation is one of the most frequent and severe challenges to living cells1. The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments2, 3, 4, 5. Remarkably, these fragments are readily reassembled into a functional 3.28-megabase genome. Here we describe the relevant two-stage DNA repair process, which involves a previously unknown molecular mechanism for fragment reassembly called \'extended synthesis-dependent strand annealing\' (ESDSA), followed and completed by crossovers. At least two genome copies and random DNA breakage are requirements for effective ESDSA. In ESDSA, chromosomal fragments with overlapping homologies are used both as primers and as templates for massive synthesis of complementary single strands, as occurs in a single-round multiplex polymerase chain reaction. This synthesis depends on DNA polymerase I and incorporates more nucleotides than does normal replication in intact cells. Newly synthesized complementary single-stranded extensions become \'sticky ends\' that anneal with high precision, joining together contiguous DNA fragments into long, linear, double-stranded intermediates. These intermediates require RecA-dependent crossovers to mature into circular chromosomes that comprise double-stranded patchworks of numerous DNA blocks synthesized before radiation, connected by DNA blocks synthesized after radiation.