Extreme genome repair

Abstract

Slade et al. (2009) describe in this issue how the genome of the bacterium Deinococcus radiodurans gets reassembled after being shattered by high-dose radiation. In contrast to the extreme nature of the damage, the steps of repair appear surprisingly ordinary. So, why can't all organisms carry out extreme genome repair?

Figure 1. Possible Modes of Fragmented DNA Repair in D. radiodurans

Slade et al. (2009) provide support for a repair mechanism called extensive synthesis-dependent strand annealing (ESDSA) (A–G). During repair, ESDSA creates extensive regions of newly synthesized single-stranded DNA (red) (E) and results in regions of newly synthesized double-stranded DNA (F and G). A PCR-like repair mechanism described in the text also fulfills both criteria. (H–J) In the conservative break-copy or break-induced replication (BIR) model of Luder and Mosig (1982), regions of new double-stranded DNA are predicted (I, parallel red lines), whereas extensive single-stranded regions are not. Black horizontal lines indicate existing strands of DNA, arrowheads mark 3′ ends, and the red “x” represents a replication-blocking DNA lesion that is repaired to leave a single-strand nick following base-excision repair.