A recent publication on regulation of RcGTA suggested the promoter click here for the gene cluster was located 215 bp upstream from the predicted orfg1 start codon . Our results with the targeted deletion of the predicted promoter sequence located ~100 bp upstream
indicate this sequence is also important for expression of the RcGTA gene cluster. The “rpoD17” deletion construct on pX2Δp contains the more distal predicted promoter sequence , and so our results could reflect a requirement for this deleted sequence that is not related to transcription initiation for this fusion. If the Rba proteins in R. capsulatus are indeed controlling the activity of a σ factor, the effect of the rbaV and rbaY mutations on colony morphology and culture viability may implicate these proteins as regulators of a σ factor with a large regulon, such as RpoD. However, the exact mechanistic functioning in this R. capsulatus Rba pathway is still unclear because of the dominant
role of RbaV and in light of the diversity of similar partner-switching modules in other species that control downstream targets other than σ factors. Nevertheless, RbaV, RbaW and RbaY are linked by their phenotypes and do affect RcGTA gene expression and production in R. capsulatus. Conclusions We have identified a set of predicted regulatory proteins that function in a common pathway to affect production of RcGTA (Figure 8). Additionally, these proteins influence stationary phase viability and colony STA-9090 in vitro morphology, indicating this system also plays other regulatory roles in R. capsulatus. Based on their homology to other proteins and the presence of conserved domains, we hypothesize that these represent a partner-switching Adenosine regulatory system that integrates control of RcGTA gene expression with other aspects of physiology in R. capsulatus. Whether or not this is mediated through the control of a cognate σ factor remains to be determined. Acknowledgements We thank S. MacLellan, N. Bykova, K. Tahlan and D. Bignell for help with the protein
experiments. This research was funded by grants from the Natural Sciences and Engineering Research Council (NSERC) (http://www.nserc-crsng.gc.ca/Index_eng.asp) and the Canada Foundation for Innovation (http://www.innovation.ca/en) to ASL. RM was supported by fellowships from NSERC and the Memorial University School of Graduate Studies (http://www.mun.ca/sgs/). Electronic supplementary material Additional file 1: Experimental strains used in this study. (DOCX 33 KB) Additional file 2: Experimental plasmids used in this study. (DOCX 35 KB) Additional file 3: Primers used in this study. (DOCX 32 KB) References 1. Marrs BL: Genetic recombination in Rhodopseudomonas capsulata . Proc Natl Acad Sci USA 1974, 71:971–973.PubMedCentralPubMedCrossRef 2. Lang AS, Zhaxybayeva O, Beatty JT: Gene transfer agents: phage-like elements of genetic exchange. Nat Rev Micro 2012, 10:472–482. 3.