Bursting onto the scene? Exploring stochastic mRNA production in bacteria

Recent large-scale measurements of gene expression variability (or noise) in E. coli have led to the unexpected conclusion that the variability is in large part dictated by and increasing with the mean level of expression. Here we review the evidence for this apparent universal trend in variability, as well as for the related idea that transcription is fundamentally bursty. We examine recently proposed mechanisms for burstiness and universality and argue that they do not explain important features of observed data. Finally, we discuss potential limitations and pitfalls in the interpretation of experimental measurements of cell-to-cell variability.