engleski

Survival of Deinococcus radiodurans in extreme conditions: genome restoration by recombination

Deinococcus radiodurans, an extremophile bacterium, sustains extreme conditions of life, such as excessive desiccation and exposure to high doses of ionizing radiation. Both desiccation and radiation cause DNA double-strand breaks, the most severe form of genomic damage. Whereas most vegetative prokaryotic and eukaryotic cells can survive less than a dozen simultaneous double-strand DNA breaks, D. radiodurans survives extreme desiccation and ionizing radiation breaking its genome into several hundred fragments. Remarkably, in just couple of hours, these fragments are reassembled into functional chromosomes due to an efficient and precise DNA repair process. We have found that genome reconstitution in D. radiodurans following gamma irradiation takes place as a two-stage process, which involves a novel mechanism called “ extended synthesis-dependent strand annealing” (ESDSA), followed and completed by conservative homologous recombination. In ESDSA, chromosomal fragments produced by radiation are used both as primers and templates for a massive synthesis of long single-strand extensions. This synthesis depends on DNA polymerase I and incorporates more nucleotides than does normal replication in intact cells. Newly synthesized single-strand extensions become “ sticky ends” that anneal with high precision, joining together contiguous DNA fragments into long linear intermediates. These intermediates are finally matured by RecA-mediated crossovers into functional circular chromosomes, comprising double-stranded patchworks of numerous DNA blocks synthesized before radiation, connected by DNA blocks synthesized after radiation.

Deinococcus radiodurans; DNA repair; DNA synthesis; recombination; ESDSA

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