DNA end resection during homologous recombination

Abstract

Exposure to environmental mutagens but also cell-endogenous processes can create DNA double-strand breaks (DSBs) in a cell's genome. DSBs need to be repaired accurately and timely to ensure genomic integrity and cell survival. One major DSB repair mechanism, called homologous recombination, relies on the nucleolytic degradation of the 5'-terminated strands in a process termed end resection. Here, we review new insights into end resection with a focus on the mechanistic interplay of the nucleases, helicases, and accessory factors involved.

Figure 1:. DSB are repaired by NHEJ or HR.

While NHEJ directly re-ligates DSBs, HR requires nucleolytic processing of the DSB ends by MRX-mediated initial and Exo1 or STR (Sgs1-Top3-Rmi1)-Dna2-mediated long-range resection. The ssDNA generated is coated by RPA and subsequently bound by the Rad51 recombinase for strand invasion and repair synthesis. The S. cerevisiae protein names are shown. See text for homologs in other organisms.

Figure 2:. “Resting state” (a) and “cutting state” (b) of the E. coli MR (SbcCD) complex.

The Mre11 subunits are in blue and purple and the Rad50 subunits are in yellow and orange. The DNA duplex in the “cutting state” is in gray. The protruding Rad50 coiled coils and the zinc hook, whose structures could not be determined due to their flexibility, are schematically depicted. Molecular surface structures are from [17] (PDB IDs 6S6V and 6S85 [59]) and were rendered with Mol* [60].

Figure 3:. Resection and the DNA damage response (DDR).

(a) Tel1 is recruited to DSBs by MRX. (b) Upon resection and RPA binding, Mec1 is recruited. Multiple DDR proteins as well as DDR-induced phosphorylation events regulate the resection nucleases both in a stimulatory and inhibitory fashion, giving rise to a complex regulatory network. Phosphorylation events (P) are colored according to the responsible kinase. White Ps denote CDK-mediated phosphorylation. Question marks denote regulations that were described for mammals but have not yet been established in other organisms. The S. cerevisiae protein names are shown. See text for homologs in other organisms.