Isolation and Characterization of σ70-Retaining Transcription Elongation Complexes from Escherichia coli

σ70 subunit is thought to be released from the core RNA polymerase (RNAP) upon the transition from initiation to elongation or shortly afterward. Here, we identify a population of RNAP from E. coli that retains σ70 throughout elongation. The relative amount of this population appears to depend on cellular growth and reaches its maximum during the stationary phase. The proportion of σ70-retaining elongation complexes (EC-σ70) is invariant with various promoters or distances from the transcription start site. EC-σ70 responds to pauses, intrinsic terminators, and the elongation factor NusA similarly to EC without σ70. However, EC-σ70 has a substantially higher ability to support multiple rounds of transcription at certain promoters, suggesting its profound role in gene expression and regulation in bacteria.