Thus, CaNik1p has to be considered as a positive regulator of Hog1p activity, similar to Dic1p from C. heterostrophus and contrary to DhNik1p

and Sln1p. This is in agreement with the earlier results that CaNik1p cannot reverse the lethal phenotype of Sln1 deletion in S. cerevisiae whereas VX-680 molecular weight DhNik1p can. However, the mechanism leading to the reduced overall phosphate transfer activity to the response regulator remains to be investigated. As long as no protein structures are available from group III histidine kinases, one cannot exclude that point mutations and protein truncation have severe effects on the protein structures. The constructed mutated versions of CaNIK1 could not be re-integrated in the available CaNIK1

homozygous deletion mutants of Candida albicans[8–18] as these mutants were constructed with the widely used URA blaster method and, thus, are prototrophic for uracil. Consequently direct transformation with the pYES2 vectors that harbor the mutated variants of the CaNIK1 was not possible as the vector contains URA3 as a selection marker. Therefore a new CaNIK1 homozygous deletion mutant has to be constructed using for example the SAT1 flipper PRI-724 mouse cassette that makes use of nourseothricin as an antibiotic selection marker. This will allow reintegration of the CaNIK1-mutated variants from this study in such mutant. Conclusion Our results show that functional HisKA, HATPase_c PJ34 HCl and REC domains of CaNik1p are essential for the antifungal activity of the selected agents activating the HOG pathway. Moreover, the expression of CaNIK1ΔHAMP in transformed S. cerevisiae was associated with growth inhibition via constitutive phosphorylation of the MAPK Hog1p. In S. cerevisiae transformed with CaNIK1, growth inhibition resulting from treatment with the selected antifungals or from deletion of all HAMP domains from the protein required both a functional

histidine kinase CaNik1p and an intact HOG pathway. Acknowledgement We thank K. Gerth, H. Steinmetz, R. Jansen (all Research group Microbial Drugs (MWIS) of the HZI, Braunschweig) for providing us with ambruticin VS3, P. P. Müller (RDIF, HZI, Braunschweig) for frequent fruitful discussions, and V. Wray (HZI, Braunschweig) for careful correction of the manuscript. This study was financially supported by a DAAD scholarship (M. El-M.) and by the Graduate School of the HZI, SB-715992 Braunschweig. MMB was supported by a fellowship from the Alexander von Humboldt Foundation. Electronic supplementary material Additional file 1: Expression of CaNIK1ΔHAMP in the strain ΔHa was confirmed after 180 min cultivation in SG-ura. The strains NIK, ΔHa and ΔHaH510 were cultivated in SG-ura for 180 min before the expression of CaNIK1, CaNIK1ΔHAMP and CaNIK1ΔHAMP (H510Q), respectively, was detected in the protein extracts via Western Blot using an anti-Flag antibody.