Gene expression in cells is a stochastic process. Experiments have shown that noise in protein levels does not decrease to zero as mean gene expression increases. The origins of the noise floor are still debated. The goal of our study was to check how several basic mechanisms affect the noise floor level. These mechanisms are: Cell-cycle dependent gene expression, translational bursting, random protein partitioning between daughter cells at division, and cell cycle desynchronization resulting in cell-cycle age distribution within the population. Our model gives analytical predictions of the existence of the noise floor and it semi-quantitatively reproduces the shapes of the experimental noise vs. protein concentration plots. We show what additional experimental information is needed for the mean-noise fitting to be unambiguous.
 J. Jędrak, A. Ochab-Marcinek, Contributions to the 'noise floor' in gene expression in a population of dividing cells, Scientific Reports, 10, 13533 (2020)