Promoter Activation by CII, a Potent Transcriptional Activator from Bacteriophage 186 [Gene Regulation]

October 7th, 2014 by Murchland, I., Ahlgren-Berg, A., Priest, D. G., Dodd, I. B., Shearwin, K. E.

The lysogeny promoting protein CII from bacteriophage 186 is a potent transcriptional activator, capable of mediating at least a 400-fold increase in transcription over basal activity. Despite being functionally similar to its counterpart in phage lambda (λ), it shows no homology at the level of protein sequence and does not belong to any known family of transcriptional activators. It also has the unusual property of binding DNA half sites that are separated by 20 base pairs, centre to centre. Here we investigate the structural and functional properties of CII using a combination of genetics, in vitro assays and mutational analysis. We find that 186CII possesses two functional domains, with an independent activation epitope in each. 186CII owes its potent activity to activation mechanisms that are dependent on both the σ70 and α C-terminal domain (αCTD) components of RNA polymerase (RNAP), contacting different functional domains. We also present evidence that like λCII, 186CII is proteolytically degraded in vivo, but unlike λCII, 186CII proteolysis results in a specific, transcriptionally inactive, degradation product with altered self-association properties.