Promoter escape with bacterial two-component sigma factor suggests retention of sigma region two in the elongation complex [Gene Regulation]

September 23rd, 2015 by Sengupta, S., Prajapati, R. K., Mukhopadhyay, J.

The transition from the formation of RNAP-promoter open complex step to productive elongation complex step involves promoter escape of RNAP. From the structure of RNAP, a promoter escape model has been proposed which suggests that the interactions between σR4 and RNAP and σR4 and DNA are destabilized upon transition to elongation. This accounts for reduced affinity of σ to RNAP and stochastic release of σ. However, as the loss of interaction of σR4 with RNAP results in the release of intact σ, assessing this interaction remains challenging to be experimentally verified. Here we study the promoter escape model using a two- component σ factor YvrI and YvrHa from Bacillus subtilis that independently contribute to the functions of σR4 and σR2 in a RNAP-promoter complex. Our results show that YvrI, that mimics σR4, is released gradually as transcription elongation proceeds whereas YvrHa that mimics σR2 is retained throughout the elongation complexes. Thus our result validates the proposed model for promoter escape and also suggests that promoter escape involves little or no change in the interaction of σR2 with RNAP.