Transcription by RNA polymerase in bacteria requires specific promoter recognition by σ factors. The major variant ••••• factor (sigma54) initially forms a transcriptionally silent complex requiring specialised ATP-dependent activators that belong to AAA+ protein family for initiation. I will present our recent crystal structure of the 450 kDa RNAP-σ54 holoenzyme at 3.8 Å, which reveals molecular details of ••••••• and its interactions with RNAP. The structure explains how ••••••• targets different regions in RNAP to exert its inhibitory function. In addition, I will explain how the AAA activator uses its ATPase activity to activate RNAP-sigma54 holoenzyme. I will also compare different RNAP systems and suggest the existence of evolutionarily conserved regulatory hotspots within RNAPs that can be targeted by a diverse range of mechanisms to fine tune transcription.