Activated CheY (CheY-P) selleckchem interacts directly with the motor of the flagella to control swimming direction. The dephosphorylation of CheY-P occurs spontaneously, only in enterobacteria this reaction is accelerated by the phosphatase CheZ. For adaptation, CheB and its antagonist CheR remove or add methyl groups to the receptors, respectively. In R. centenaria, the two central components of the chemotactic signal transduction cascade, namely CheA and CheY, are present as the fusion protein Rc-CheAY located in the first chemotactic operon [17], a situation that is also observed in Salubrinal manufacturer Helicobacter [18]. Whereas the role

of the CheY-domain of the CheAY protein in H. pylori seems to be a phosphate sink, in R. centenaria, the function of Rc-CheAY remains still unclear. While Che proteins are generally involved in chemotactic responses, they were also shown to affect the phototactic response in R. centenaria as demonstrated by the analysis of many che mutants [19]. In the last decade, bacterial photoreactive proteins like phytochromes, previously thought to be a unique feature in plants, have been identified as photoactive yellow proteins (Pyp) and have now been extensively studied in a variety of eubacterial species (for review see [20, 21]). For R. centenaria, a Pyp-like protein, Ppr, was described in 1999 by Bauer and colleagues

[22]. The large fusion protein Ppr consists of three Veliparib manufacturer functional domains, an N-terminal Pyp domain with the cinnamic acid chromophore, the central phytochrome-like

bilin attachment domain Bbd and the C-terminal histidine kinase domain Pph which autophosphorylates Morin Hydrate an essential histidine residue [22]. Although some Pyp proteins have been crystallized and biophysically characterized in great detail (reviewed by [21]), no distinct physiological role could be attested to these unique proteins. A Ppr-deletion mutant lacking amino acid residues 114-750 did not show any alterations in phototactic behaviour, instead exhibited a strongly deregulated expression of the chalcone synthase gene suggesting a regulatory function in the polyketide synthesis [22]. Although there is no obvious direct involvement of Ppr in the phototactic or scotophobic reaction, an interaction with the chemotactic signal transduction components is plausible to regulate general phosphorylation levels or transduce phosphoryl groups to a yet unknown light-dependent signal transducing protein. We therefore analysed whether the Ppr protein and in particular its phosphorylating kinase domain Pph interacts with the Rc-Che proteins. Results The chemotactic response of E. coli is inhibited by the expression of Ppr The chemotactic network in E. coli is very sensitive to alterations in the expression level and stoichiometry of the chemotactic proteins Ec-CheW [23, 24] and Ec-CheA [25] as well as the MCP receptors [26, 27].