Figure 7.
Gyrase with a single CTD undergoes DNA-induced N-gate narrowing. Single-molecule FRET histograms for gyrase (BE17CA·BE17CAΔCTD) labeled with donor and acceptor fluorophores at the N-gate in the absence (A) and presence of 2 mM ADPNP (B) or 20 nM plasmid DNA (C). In the absence of DNA or ADPNP, the FRET efficiency is low (EFRET = 0.2), consistent with an open N-gate. ADPNP addition leads to N-gate closure, evidenced by a shift of the FRET efficiency to EFRET = 0.95–1. In the presence of DNA, the FRET efficiency is also high (EFRET = 0.95–1), which is consistent with DNA-induced narrowing of the N-gate. n denotes the number of events summarized in each histogram.