Promoter-centered model of gene expression. (A) All the complex molecular interplay between an arbitrary number of TFs is described generically while the subsequent steps of gene expression are kept simple but explicit. (B) Promoter state fluctuations determine the time-dependent transcriptional efficiency X(t) that propagates successively to RNA level R(t) and protein level P(t) through coupled stochastic synthesis/degradation processes. In this example with realistic timescales and parameter values (cf table S1 of Additional file 1 for a complete description), TFs A and B cooperate and the closed state of chromatin C compete with their association. The highest and lowest transcription rates correspond respectively to open chromatin with A and B bound to the promoter and closed chromatin. (C) This model can represent many different aspects of regulation (see Description ability) making it relevant for describing either prokaryotic or eukaryotic systems.