Figure 2.

ATM-dependent signalling events around DSBs in different chromatin environments. (a) ATM's role in DSB repair within transcriptionally silent heterochromatin involves KAP-1 phosphorylation (KAP-1^S824p), promoting CHD3.1 dispersal. ATM-dependent RNF20-RNF40 activity, at the same time, promotes H2B^K120ub and ACF1-SNF2H recruitment to adjust nucleosome spacing to make chromatin amenable to DSB repair. (b) In response to nucleolar DSBs (i.e. transcriptionally active regions) ATM generates TCOF^S1199p, which facilitates NBS1 translocation into the nucleolus. Once there, NBS1 inhibits RNA Pol I globally, enabling DSB repair by NHEJ. Outside the nucleolus, RNA Pol II activity is attenuated by ATM, via BAF180^S948p phosphorylation, precluding chromatin decompaction during transcription. ATM-dependent PRC1/2 recruitment facilitates H2A^K119ub, which augments this process. (Online version in colour.)