Orthologues of whiA are found in most Gram-positive bacteria and their gene products have a bipartite structure consisting of a domain similar to a class of homing endonucleases combined with a DNA-binding domain in the shape of a helix-turn-helix motif [19–21]. S. coelicolor WhiA is so far reported to bind directly to its own promoter and to a sporulation-induced promoter controlling the parAB genes [22]. WhiB is the

founding member of the actinomycete-specific Wbl (WhiB-like) family of FeS-cluster proteins that appear to act in transcription control, although functions ascribed to Wbl proteins have been controversial [4, 23–26]. Disruption of whiA or whiB arrests sporulation at a very early stage, and mutant phenotypes of the two are indistinguishable [15, 19, 23]. The two converging Geneticin in vivo pathways that depend on whiG-whiI/whiH and whiA/whiB,

respectively, are required for controlling most aspects of the conversion Quisinostat mouse of aerial hyphae into spores. However, very few click here direct targets are known for these central regulatory whi genes, and overall it seems like only a small subset of genes involved in aerial hyphal sporulation have been identified. In order to find further genes that are developmentally regulated in S. coelicolor and involved in the differentiation of aerial hyphae to spores, we have carried out a DNA microarray-based transcriptome analysis. The experiment was designed to identify genes that are up-regulated during development of the wild-type parent but are not up-regulated in derivative strains bearing mutations in either whiA or whiH, representing the two abovementioned sporulation-specific pathways. For a subset of the genes that were identified as developmentally regulated and specifically affected by whiA and/or whiH, we have confirmed expression patterns using real-time qRT-PCR, S1 nuclease IKBKE mapping, and reporter gene fusions, and constructed and analysed deletion

mutants. This has identified a set of previously unknown developmentally regulated promoters and sporulation genes that encode different types of regulators, a protease, an L-alanine dehydrogenase, and proteins related to spore pigment biogenesis. Results and discussion Transcriptional analysis of whiA- and whiH-dependent gene expression during development of S. coelicolor A developing S. coelicolor colony is a complex mixture of cells at different developmental stages, and the sporulating aerial mycelium constitutes only a fraction of the total colony biomass. In order to identify genes that are specifically changed in sporulating aerial hyphae, we have therefore compared the pattern of gene expression in the wild-type strain M145 to those in two developmental mutants lacking the regulatory genes whiA or whiH (strains J2401 and J2408, respectively). Disruption of these genes imposes specific blocks or defects at an early stage of aerial hyphal sporulation without overtly affecting any other cell type.