Stochastic transcriptional pulses orchestrate flagellum biosynthesis in E. coli

Abstract

The classic picture of flagellum biosynthesis in E. coli, inferred from population measurements, describes a tightly controlled, deterministic transcriptional program. In individual E. coli cells, we discover that flagellar promoters are in fact stochastically activated in pulses. Such pulses comprise coordinated on and off states of promoter activity, each of which can span multiple generations. We demonstrate that this pulsing program obeys the regulatory logic of flagellar assembly, which dictates whether some promoters skip pulses. Remarkably, pulses in this transcriptional network appear to be actually governed by a post-translational circuit. Our results suggest that even topologically simple transcriptional networks can generate unexpectedly rich temporal dynamics and phenotypic heterogeneities.