Contribution of ​RNA polymerase concentration variation to protein expression noise

2014-09-01 22:31
Cell-to-cell variation in gene expression, or noise, is a general phenomenon observed within cell populations. Transcription is known to be the key stage of gene expression where noise is generated, however, how variation in ​RNA polymerase (​RNAP) concentration contributes to gene expression noise is unclear. Here, we quantitatively investigate how variations in absolute amounts of ​RNAP molecules affect noise in the expression of two fluorescent protein reporters driven by identical promoters. We find that intrinsic noise is independent of variation in ​RNAP concentrations, whereas extrinsic noise, which is variation in gene expression due to varying cellular environments, scales linearly with variation in ​RNAP abundance. Specifically, the propagation of ​RNAP abundance variation to expressed protein noise is inversely proportional to the concentration of ​RNAP, which suggests that the change in noise that results from ​RNAP fluctuations is determined by the fraction of promoters that is not occupied by ​RNAP.