Sensing and responding to diverse extracellular signals? Analysis of the sensor kinases and response regulators of Streptomyces coelicolor A3(2)

Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK Correspondence Matthew I. Hutchings matt.hutchings{at}bbsrc.ac.uk Streptomyces coelicolor is a Gram-positive soil bacterium that undergoes a complex developmental life cycle. The genome sequence of this organism was recently completed and has revealed the presence of over 60 sigma factors and a multitude of other transcriptional regulators, with a significant number of these being putative two-component signal transduction proteins. The authors have used the criteria established by Hoch and co-workers (Fabret et al ., 1999, J Bacteriol 181, 1975–1983) to identify sensor kinase and response regulator genes encoded within the S. coelicolor genome. This analysis has revealed the presence of 84 sensor kinase genes, 67 of which lie adjacent to genes encoding response regulators. This strongly suggests that these paired genes encode two-component systems. In addition there are 13 orphan response regulators encoded in the genome, several of which have already been characterized and are implicated in development and antibiotic production, and 17 unpaired and as yet uncharacterized sensor kinases. This article attempts to infer useful information from sequence analysis and reviews what is currently known about the two-component systems, unpaired sensor kinases and orphan response regulators of S. coelicolor from both published reports and the authors' own unpublished data. The online version of this review (at http://mic.sgmjournals.org ) contains supplementary figures showing results from the alignment of residues surrounding conserved histidine residue in SKs, and from TopPred 2 analysis predicting the membrane topology of all 84 SK sequences.