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. Author manuscript; available in PMC: 2011 Dec 1.
Published in final edited form as: Nat Chem Biol. 2011 May 8;7(6):367–374. doi: 10.1038/nchembio.561

Figure 4.

Figure 4

λ exo performs distributive degradation before complete engagement to DNA. (a–b) Representative single molecule time traces of the acceptor and donor channel signals obtained from using the extended construct (used in Fig. 3) but in the presence of 6 nM (a) and 60 nM (b) CoA-547-labeled protein. Multiple events of increase and decrease in donor channel signal are observed before FRET starts to increase upon degradation beyond the first 23 bp. Note that the binding/unbinding events do not occur once the processive phase starts, showing that the events observed are specific to the distributive phase. (c) Average degradation time of the first 23 bp of the extended construct determined from the time between protein addition and the moment that FRET starts to increase (see the magenta arrows). (d) Average frequency of donor intensity increase/decrease events before FRET starts to increase. (e) Model of DNA degradation of λ exo. The degradation activity of λ exo is divided into three phases: initiation, distributive, and processive degradation.