Figure 5.

Real-time observation of single RNA molecule conformational changes on buffer exchange. (a) Schematics of the experimental apparatus showing how buffer is directly introduced on the area under observation to reduce the mixing time. (b) Time traces (integration time, 5 ms) of donor (solid line) and acceptor signal (dotted line) on buffer exchange. [Mg²⁺] was alternated between 0 and 1 mM every 200 ms (starting from 0). Significant donor signal reduction is seen every time Mg²⁺ buffer is present. Vertical grids denote buffer exchange periods (400 ms). Three-point averaging was applied to reduce noise. Donor photobleaching is marked by an arrow. (c) The average proximity factor over seven periods. The nominal arrival times for the buffer without Mg²⁺⁺ and with 1 mM Mg²⁺⁺ are at time = 0 and 200 ms. The transition is not abrupt because of the finite mixing time between the two buffers.