Multiplicity of DNA end resection machineries in chromosome break repair

Abstract

DNA end resection is critical for chromosome break repair by homologous recombination and influences the efficiency of repair by nonhomologous DNA end joining. An elegant study by Sinha and colleagues (pp. 1423-1437) published in the June 15, 2009, issue of Genes & Development identified a novel mycobacterial DNA end resection protein complex, AdnAB, that harbors dual DNA motor and dual nuclease functions. Sinha and colleagues also demonstrated that the DNA end-binding protein complex Ku regulates the activity of AdnAB.

Figure 1.

DSB end resection in prokaryotes by the RecBCD (A), RecQ–RecJ (B), and AddAB (C) helicase–nuclease ensembles. Short DNA fragments released by nucleolytic cleavage are indicated by dashed lines. See the text for details.

Figure 2.

Interplay between AdnAB and Ku during DSB processing in mycobacteria. Ku and AdnAB compete for binding to DSB ends. If Ku binds the DNA ends first, access to AdnAB is limited, thus favoring repair by NHEJ. If AdnAB is allowed to engage the DNA ends, 5′ resection occurs to expose 3′ ssDNA tails that are used to assemble the RecA presynaptic filament, and repair of the DSB occurs by HR. If the 3′ ssDNA tails are trimmed, subsequent repair by NHEJ will result in deletions at the DSB site.