Contrary to the classical view for transcription, where RNA polymerases track along the chromatin template, we view polymerases as transiently immobilized in larger structures called transcription factories. As a consequence of this, the molecular machine (polymerase) is fixed, and the chromatin template now moves, as it is being reeled to be transcribed.

    This makes RNA polymerases a critical tie for the 3-D architecture of eukaryotic genomes, organizing it into loops of variable sizes.

    For an overview of a typical transcription cycle, from promoter diffusion and initiation, through elongation, and up  to termination, see the cartoon (above) and the movie (left).