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Members of the prokaryotic genus Streptomyces produce over 60% of all known antibiotics and a wide range of industrial enzymes. A leading theme in microbiology is which signals are received and transmitted by these organisms to trigger the onset of morphological differentiation and antibiotic production. The small ␥-butyrolactone A-factor is an important autoregulatory signaling molecule in streptomycetes, and A-factor mutants are blocked in development and antibiotic production. In this study we showed that heterologous expression of the 324-amino acid secreted regulatory protein Factor C resulted in restoration of development and enhanced antibiotic production of an A-factor-deficient bald mutant of Streptomyces griseus, although the parental strain lacks an facC gene. Proteome analysis showed that in the facC transformant the production of several secreted proteins that belong to the A-factor regulon was restored. HPLC-MS/MS analysis indicated that this was due to restoration of A-factor production to wild-type levels in the transformant. This indicates a connection between two highly divergent types of signaling molecules and possible interplay between their regulatory networks.

TPPP/p25, a flexible unstructured protein, binds to tubulin and induces aberrant microtubule assemblies. We identified hereby glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a new interacting partner of TPPP/p25. The immunoprecipitation and affinity chromatographic experiments with bovine brain cell-free extract revealed that the interaction was salt and NAD + sensitive while ELISA showed resistant and firm association of the two isolated proteins. In transfected HeLa cells at low expression level of EGFP-TPPP/p25, while the green fusion protein aligned at the microtubular network, GAPDH distributed uniformly in the cytosol. However, at high expression level, GAPDH co-localized with TPPP/p25 in the aggresome-like aggregate. Immunohistochemistry showed enrichment of TPPP/ p25 and GAPDH within the a-synuclein positive Lewy body.

The small ␥-butyrolactone A-factor is an important autoregulatory signaling molecule for the soil-inhabiting streptomycetes. Starvation is a major trigger for development, and nutrients are provided by degradation of the vegetative mycelium via a process of programmed cell death, reusing proteins, nucleic acids, and cell wall material. The A-factor regulon includes many extracellular hydrolases. Here we show via proteomics analysis that many nutrientscavenging and stress-related proteins were overexpressed in an A-factor non-producing mutant of Streptomyces griseus B-2682. Transcript analysis showed that this is primarily due to differential transcription of the target genes during early development. The targets include proteins relating to nutrient stress and environmental stress and an orthologue of the Bacillus sporulation control protein Spo0M. The enhanced expression of these proteins underlines the stress that is generated by the absence of A-factor. Wild-type developmental gene expression was restored to the A-factor non-producing mutant by the signaling protein Factor C in line with our earlier observation that Factor C triggers A-factor production.

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