Skip to main content
. 2017 Oct 23;45(21):12401–12412. doi: 10.1093/nar/gkx974

Figure 7.

Figure 7.

Model for transcription rate control during the cell cycle in eukaryotes with symmetric and asymmetric cell division. In symmetrically dividing cells, such as human fibroblasts and S. pombe, RNA pol II is much less concentrated than their DNA targets. As there is a strong bias of the equilibrium toward the bound state (kon >> koff), all the RNA pol II molecules are bound to chromatin and nTR is strictly dependent on the RNA pol II number of molecules (Scenario #1). In asymmetrically dividing cells, such as S. cerevisiae, nTR does not depend on the RNA pol number of molecules, either because there is a vast excess of them over their targets (e.g. for RNA pol I+III) in which it becomes dependent on the number of DNA targets number (Scenario #2), or because the RNA pol concentration is regulated in such a way that it varies with cell volume (represented as an v superscript in the figure). This scenario (#3) corresponds to RNA pol II. In it nTR is constant and proportional to the actual number of active RNA pol II molecules. Note that scenarios #1 and #3 allow the regulation of the nascent transcription rate by controlling the concentration of RNA pol II, whereas scenario #2 does not allow regulation at the RNA polymerase level because it is in vast excess.