Two-step mechanism of DNA repair in D Two-step mechanism of DNA repair in D. radiodurans shattered by ionizing radiation. Two-step mechanism of DNA repair in D. radiodurans shattered by ionizing radiation. Several genomic copies of D. radiodurans undergo random DNA double-strand breakage, producing numerous fragments (step 1). The fragmented DNA is recessed in a 5′-to-3′ direction, presumably by RecJ, liberating single-stranded 3′ overhangs (step 2), which, through RecA- and RadA-mediated strand invasion, prime synthesis on overlapping fragments through a migrating D loop (step 3). DNA synthesis is initiated by Pol III (step 4) and elongated by Pol III, with Pol I filling up gaps arising from the excision repair of damaged bases (A), or by Pol I alone (B).Two noncontiguous fragments are linked by convergent elongations on a third “bridging” fragment (step 5). Newly synthesized single strands dissociate from the template (step 6) and anneal to complementary single-stranded extensions, forming dsDNA intermediates (step 7). The flaps are removed (by SbcCD?), and the gaps are filled (by Pol I?) (step 8). Long linear intermediates are joined into circular chromosomes by RecA-dependent crossovers (step 9). (Modified from reference 572 with permission from Elsevier and based in part on data from reference 676.)‏ Dea Slade, and Miroslav Radman Microbiol. Mol. Biol. Rev. 2011; doi:10.1128/MMBR.00015-10