Transcription Loops Video

The cartoon shows how transcription initiation and termination of a highly expressed gene lead to formation and disappearance of a transcription loop. The sequence of the events:

• a gene body (orange thread) is coiled within a locus (blue threads) in a compact structure;
• upon transcription initiation, RNAPIIs (dark grey oval structures) are loading at the gene promoter (red) and begin to elongate;
• during elongation, nRNPs appear and grow in size (depicted as grey amorphous structures);
• during a transcription pause, chromatin of the gene is coiled and forms a sliding knot (orange thread), dynamically formed beyond the last RNAPII of the first burst and disentangled by first RNAPII of the second burst;
• dense decoration with voluminous nRNP rigidifies the gene axis and forces its expansion, as well as the divergence of gene flanks (blue threads);
• RNAPIIs of the first transcription burst reach the 3’ gene end, release attached nRNPs and dissociate from the gene;
• the sliding chromatin knot reaches the 3’ gene end;
• RNAPIIs stop loading at the promoter at the end of the second burst;
• gene condensation starts 5’-terminally;
• the gene flanks begin to converge;
• the gene returns to its coiled compact state.

Animation: Irina Solovei, Jack Bates, Susanne Leidescher and artists Dimitar Kralev & Tamako Suzuki