Figure 3.

Repair of DSBs in heterochromatin. Four possible mechanisms exist for the repair of DSBs. Fast c-NHEJ (purple arrow) involves the religation of broken ends in a Ku70/80-dependent process. DSBs that cannot be repaired quickly might be those present in heterochromatin (HC), or might be breaks occurring in euchromatin that are sequestered into HC for protection (red arrow). In order for repair to take place, the DSBs are relocated on the surface of the HC (brown arrow). These breaks can be repaired with slow kinetics by resection-mediated c-NHEJ, involving the nuclease Artemis (blue arrows). In mice and under certain conditions (see text for details), DSBs can be repaired by alt-NHEJ (orange arrows). In G2, if NHEJ is unable to repair DSBs, there is further resection with repair occurring via HR (either gene conversion or single-strand annealing, see Figure 2) (green arrows). Red dots indicate histone H2AX phosphorylation (γH2AX). For key to other histone modifications see Figure 2.