Evidence for self-association of the alternative sigma factor σ54

Sigma factor sigma 54 has a distinct modus operandi for mediating the activation of bacterial RNA polymerase (RNAP) at promoter recognition motifs 12 and 24bp upstream from transcription start sites. sigma 54 was thought to act as monomer in all transcription steps. However, we provide evidence that sigma 54 of Pseudomonasputida interacts stably with itself. The interface between monomers involves contacts in sigma 54 regions I and III, sequences that play key roles in the transcription activation of sigma 54RNAP holoenzyme. These roles include interactions with activator proteins and the 12 and 24 motifs. In particular, we detected inter-monomer contacts between regionI, and between regionI and the Cterminal portion of regionIII. Our results suggest a new auto-antagonistic regulatory state of sigma 54. Structured digital abstract sigma 54 and sigma 54 bind by molecular sieving (View Interaction: 1, 2) sigma 54 and sigma 54 bind by blue native page (View interaction) P. aeruginosa sigma 54 physically interacts with P. aeruginosa sigma 54 by two hybrid (View interaction) sigma 54 physically interacts with sigma 54 by two hybrid (View Interaction: 1, 2, 3) p53 physically interacts with SV40T by two hybrid (View interaction).