A. Cartoon of reporter construct (Tang et al., 2013) in which induction of the mCherry-tagged FokI endonuclease (with 4-OHT) results in double-strand break (DSBs) in a region upstream of a doxycycline-inducible reporter gene (YFP-MS2). Ongoing transcription of the reporter gene can be visualized by the presence of a YFP-MS2 fusion protein that binds stem-loop structures in the nascent transcript. 