Movie S3.

Unwinding of a λ DNA molecule in a solution of 40 nM RecQ and AF488SSB at 37 °C. Initially, the DNA is not seen due to the absence of fluorescent dye. A white arrow indicates initiation of a class 2 unwinding fork that then moves in a bidirectional fashion as indicated by the cyan (left end) and red (right end) arrows. The flow, when on, is from left to right in the movie and the RecQ and AF488SSB fill the channel 33 s into the movie. The elapsed time is indicated in hours:minutes:seconds. (Scale bar, 5 μm.)