Transcribing Supercoils

This image of RNA polymerase transcribing supercoils was created by Nello Bossi.

You can download the original quicktime movie from here in BinHex format.
Note that if you have problems, on a mac hold the mouse button down on the link or on a Windows machine right-click and then choose "Save link as".

Rob Edwards also created two animated gif images from the original. The faster image has a frame delay of 0.1 secs and is essentially the same as the movie, and the slower image has a frame delay of 0.5 secs. Both should be displayed in your browser.

This is the original description from Nello:

Dear friends & colleagues

We thought that you might like viewing the attached document: a short
animated sequence - a "Quicktime" movie (our apologies to non-Mac users) -
portraying a model (yes, a model) of how RNA polymerase could manage to
read a double stranded helical template (often negatively supercoiled)
without the nascent RNA becoming irremediably entangled around the DNA. [We
remind you that the displacement of the transcription bubble along the
template requires rotation of the bubble around the template axis]. The
model proposes that binding of RNA polymerase to the promoter and formation
of the transcription bubble "inoculates" the formation of a plectonemic
supercoiled branch that extrudes as transcription goes on. Maintenance of
an apical position by RNA polymerase prevents RNA/DNA entanglement. The
movie is largely inspired by the electron micrographs of 
 ten Heggeler-Bordier et al. EMBO J 11, 667-672 (1992). In the animated
sequence, the template is a small negatively supercoiled circular DNA
molecule. The transcribed region spans roughly one-fourth of the circle.
You have the right to three complete transcription cycles (those of you who
have a QuickTime Movie Player application with a "loop" function available,
can have it running indefinitely).

Nello

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