Checkpoint inhibition of origin firing prevents DNA damage globally but in particular at convergently transcribed gene pairs. (A) Graphs of γH2A ChIP from the indicated strains released from G1 phase arrest into 200 mM HU for 90 min. The graphs are the average γH2A ChIP signal centered on all origins (left), or origins split into early firing (Trep < 27.5 min, middle), or late firing (Trep > 27.5 min, right). Data are normalized to the ChIP signal of unmodified H2A. (B) Chromosomal view of data from A; only chromosome XI is shown for simplicity. Orange and black arrows indicate origins that fire efficiently in the sld3-A dbf4-A strain, while the pink arrow indicates an origin that does not fire efficiently in the sld3-A dbf4-A strain. (C,D) Schematic diagram of origins between convergently transcribed gene pairs (C, top), or between codirectional/divergent gene pairs (D, top). (Bottom) γH2A ChIP signal from A was normalized to the amount of replication at that locus. These data were binned according to average time of replication in a normal S-phase (Trep) and separated into those origins that are between convergently transcribed gene pairs (C) or nonconvergent gene pairs (D).