Fig. 1: In steady state, periods of transcriptional activity (ON) are interrupted by periods of inactivity (OFF).

a Graph for the kinetic proofreading of activator identity¹⁰. The promoter is depicted as a box, the bound transcriptional activator by a black triangle, a repressor (e.g., nucleosome) whose removal (delay step) is required for transcription by a gray dot. Arrows (directed edges) indicate allowed transitions between microstates. Different arrow lengths indicate that clockwise transitions are statistically preferred over counterclockwise transitions due to the transfer of free energy to the system in the transition from repressed to derepressed promoter in the presence (but not absence) of the activator and its dissipation upon return to the repressed state. b Scheme of the modified PHO5 gene (top) and chromophore gene (bottom). PHO5 contained a tetradecamer of the binding sequence for the PP7 coat protein (PCP). PCP was expressed as a fusion with a green fluorescent protein (GFP) with nuclear localization signal (NLS) under the control of the RPS2 promoter (bottom). The cartoon of budding cells (in gray) shows that nuclear GFP is concentrated at the site of PHO5 transcription. c Left panel column: Examples of single-cell fluorescence time series for wild type, isw2\(\Delta\), chd1\(\Delta\), and pho4\(\Delta\)[75–90]. Right panel column: Each box contains 100 binary time series obtained from change point detection analysis of fluorescent time series and ordered in the sequence of increasing time between the beginning of the observational time window and the onset of the first ON period. Horizontal black lines indicate the length of ON periods, white lines the length of OFF periods, which often spanned the entire width of the observational time window.