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A tetR family transcriptional regulatory gene (SCO1712) was identified as a global antibiotic regulatory gene from a Streptomyces interspecies DNA microarray analysis. SCO1712 disruption in Streptomyces coelicolor not only upregulated antibiotic biosynthesis through pathway-specific regulators when a previously identified pleiotropic downregulatory wblA was expressed but also further stimulated antibiotic production in a wblA deletion mutant, implying that SCO1712 might encode a novel antibiotic downregulator.

RNase III family enzymes, which are perhaps the most widely conserved of all ribonucleases, are known primarily for their role in the processing and maturation of small RNAs. The RNase III gene of Streptomyces coelicolor, which was discovered initially as a global regulator of antibiotic production in this developmentally complex bacterial species and named absB (antibiotic biosynthesis gene B), has subsequently also been found to modulate the cellular abundance of multiple messenger RNAs implicated in morphological differentiation. We report here that regulation of differentiation-related mRNAs by the S. coelicolor AbsB/RNase III enzyme occurs largely by ribonucleolytic cleavage of transcripts encoding the pleiotropic transcription factor, AdpA, and that AdpA and AbsB participate in a novel feedback-control loop that reciprocally regulates the cellular levels of both proteins. Our results reveal a previously unsuspected mechanism for global ribonuclease-mediated control of gene expression in streptomycetes.

The Streptomyces coelicolor absB gene encodes an RNase III family endoribonuclease and is normally essential for antibiotic biosynthesis. Here we report that AbsB controls its own expression by sequentially and site specifically cleaving stem-loop segments of its polycistronic transcript. Our results demonstrate a ribonucleolytic regulatory role for AbsB in vivo.

The filamentous bacterium, Streptomyces coelicolor, undergoes a complex cycle of growth and development in which morphological differentiation coincides with the activation of the orphan response regulator RamR and the biosynthesis of a morphogenic peptide called SapB. SapB is a lantibiotic-like molecule derived from the product of the ramS gene that promotes formation of aerial hyphae by breaking the aqueous tension on the surface of the substrate mycelium. A ramR-disrupted mutant is delayed in aerial hyphae formation while constitutive overexpression of ramR accelerates aerial hyphae formation in the wild-type strain and restores SapB biosynthesis and aerial hyphae formation in all developmental mutants (bld) tested. Using DNA microarrays to globally identify S. coelicolor genes whose transcription was affected by ramR mutation or overexpression, we discovered a ramR-activated locus of contiguous cotranscribed developmental genes that modulate both aerial hyphae formation and sporulation. The genes of this cluster of ramR-activated genes (rag), which are chromosomally distant from previously known RamR-regulated genes, include: ragA (sco4075) and ragB (sco4074), which encode two subunits of an ABC transporter, ragK (sco4073), a putative histidine kinase, and ragR (sco4072), a ramR paralogue. Promoter mapping and protein-DNA binding experiments indicate that RamR activates ragABKR transcription directly, by binding to three sequence motifs in the ragABKR promoter region. A constructed ragABKR null mutant was able to synthesize SapB and erect aerial hyphae; however, these hyphae were unusually branched, reminiscent of substrate hyphae. Subsequent stages of differentiation, septation and sporogenesis were delayed. The role of ragABKR in aerial hyphae formation was shown both by epistasis (ragR-activated aerial hyphae formation in bld mutants) and extracellular complementation (ragR-induced synthesis of an activity allowing aerial hyphae formation in bld mutants) experiments. In conclusion, the ragABKR locus activates a SapB-independent developmental pathway that is involved in both aerial hyphae formation and sporulation, serving to integrate sequential morphogenic changes.

A complex programme of regulation governs gene expression during development of the morphologically and biochemically complex eubacterial genus Streptomyces. Earlier work has suggested a model in which 'higher level' pleiotropic regulators activate 'pathway-specific' regulators located within chromosomal gene clusters encoding biosynthesis of individual antibiotics. We used mutational analysis and adventitious overexpression of key Streptomyces coelicolor regulators to investigate functional interactions among them. We report here that cluster-situated regulators (CSRs) thought to be pathway-specific can also control other antibiotic biosynthetic gene clusters, and thus have pleiotropic actions. Surprisingly, we also find that CSRs exhibit growth-phase-dependent control over afsR2/afsS, a 'higher level' pleiotropic regulatory locus not located within any of the chromosomal gene clusters it targets, and further demonstrate that cross-regulation by CSRs is modulated globally and differentially during the S. coelicolor growth cycle by the RNaseIII homologue AbsB. Our results, which reveal a network of functional interactions among regulators that govern production of antibiotics and other secondary metabolites in S. coelicolor, suggest that revision of the currently prevalent view of higher-level versus pathway-specific regulation of secondary metabolism in Streptomyces species is warranted.

Based on the chromosomal locations of genes inferred from sequence analysis to be essential for the viability of Streptomyces coelicolor, Bentley et al. [Bentley, S.D., et al. 2002. Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2), Nature 417, 141-147.] have suggested that a 4.9 Mb central region of the linear S. coelicolor chromosome encodes 'core' functions expressed during vegetative growth of this species, while 1.5 Mb and 2.3 Mb chromosomal DNA segments lateral to this core encode auxiliary functions proposed to be required under other growth conditions. To examine this hypothesis and experimentally identify genes expressed during vegetative growth of S. coelicolor cultures, we used DNA microarrays to measure globally the abundance of S. coelicolor transcripts in cells growing in liquid medium. We found that, overall, genes corresponding to the 4.9 Mb core region of the S. coelicolor M145 chromosome were more highly expressed under non-limiting growth conditions than genes in the 1.5 Mb left and 2.3 Mb right chromosome arms, supporting the notion of the core versus auxiliary organization of genes on the chromosome. To examine how this chromosomal distribution of transcripts changes under other growth conditions, we also measured gene expression changes during stationary phase and several stress conditions. During stationary phase, the composition of S. coelicolor transcripts appears to shift from large quantities of growth-related transcripts encoded in the core region to those of less characterized genes, which may be essential for differentiation and other physiological responses, encoded throughout the chromosome. After temperature and osmotic upshifts, we found that S. coelicolor transiently induces a set of several hundred genes located throughout the chromosome, which may function in response mechanisms common to the two stress conditions.

A complex programme of regulation governs gene expression during development of the morphologically and biochemically complex eubacterial genus Streptomyces. Earlier work has suggested a model in which ‘higher level’ pleiotropic regulators activate ‘pathway-specific’ regulators located within chromosomal gene clusters encoding biosynthesis of individual antibiotics. We used mutational analysis and adventitious overexpression of key Streptomyces coelicolor regulators to investigate functional interactions among them. We report here that cluster-situated regulators (CSRs) thought to be pathway-specific can also control other antibiotic biosynthetic gene clusters, and thus have pleiotropic actions. Surprisingly, we also find that CSRs exhibit growth-phase-dependent control over afsR2/afsS, a ‘higher level’ pleiotropic regulatory locus not located within any of the chromosomal gene clusters it targets, and further demonstrate that cross-regulation by CSRs is modulated globally and differentially during the S. coelicolor growth cycle by the RNaseIII homologue AbsB. Our results, which reveal a network of functional interactions among regulators that govern production of antibiotics and other secondary metabolites in S. coelicolor, suggest that revision of the currently prevalent view of higher-level versus pathway-specific regulation of secondary metabolism in Streptomyces species is warranted. [ABSTRACT FROM AUTHOR]

The chromosomes of several widely used laboratory derivatives of Streptomyces coelicolor A3(2) were found to have 1.06 Mb inverted repeat sequences at their termini (i.e. long-terminal inverted repeats; L-TIRs), which are 50 times the length of the 22 kb TIRs of the sequenced S. coelicolor strain M145. The L-TIRs include 1005 annotated genes and increase the overall chromosome size to 9.7 Mb. The 1.06 Mb L-TIRs are the longest reported thus far for an actinomycete, and are proposed to represent the chromosomal state of the original soil isolate of S. coelicolor A3(2). S. coelicolor A3(2), M600 and J1501 possess L-TIRs, whereas approximately half the examined early mutants of A3(2) generated by ultraviolet (UV) or X-ray mutagenesis have truncated their TIRs to the 22 kb length. UV radiation was found to stimulate L-TIR truncation. Two copies of a transposase gene (SCO0020) flank 1.04 Mb of DNA in the right L-TIR, and recombination between them appears to generate strains containing short TIRs. This TIR reduction mechanism may represent a general strategy by which transposable elements can modulate the structure of chromosome ends. The presence of L-TIRs in certain S. coelicolor strains represents a major chromosomal alteration in strains previously thought to be genetically similar. [ABSTRACT FROM AUTHOR]

Summary: Previous work has detected an RNase E-like endoribonucleolytic activity in cell extracts obtained from Streptomyces. Here, we identify a Streptomyces coelicolor gene, rns, encoding a 140 kDa protein (RNase ES) that shows endoribonucleolytic cleavage specificity characteristic of RNase E, confers viability on and allows propagation of Escherichia coli cells lacking RNase E and accomplishes RNase E-like regulation of plasmid copy number in E. coli. However, notwithstanding its complementation of rne-deleted E. coli, RNase ES did not accurately process 9S rRNA from E. coli. Additionally, whereas RNase E is normally required for E. coli survival, rns is not an essential gene in S. coelicolor. Deletion analysis mapped the catalytic domain of RNase ES near its centre and showed that regions located near the RNase ES termini interact with an S. coelicolor homologue of polynucleotide phosphorylase (PNPase) – a major component of E. coli RNase E-based degradosomes. The interacting arginine- and proline-rich segments resemble the C-terminally located degradosome scaffold region of E. coli RNase E. Our results indicate that RNase ES is a structurally shuffled RNase E homologue showing evolutionary conservation of functional RNase E-like enzymatic activity, and suggest the existence of degradosome-like complexes in Gram-positive bacteria.. [ABSTRACT FROM AUTHOR]

Earlier work has shown that the afsfR genetic locus promotes formation of the pigmented antibiotics actinorhadin and undecylprodiglosin in Streptomyces lividans and its close relative, Streptomyces coelicolor. A protein designated as AfsR has been implicated in this activity. We report here the existence of a previously unknown gene, afsR2, which is separate from and adjacent to the AfsR-encoding sequence and which, when present at high copy number, (i) stimulates transcription of biosynthetic and regulatory genes in the actinorhodin gene cluster (act), and (ii) stimulates the synthesis of undecyiprodigiosin. We show that the effects of afsR2 on actinorhodin synthesis are mediated through transcription of the acni-0RF4 locus, which encodes a transcriptional activator of other genes in the act cluster. Analysis of the cloned afsR2 gene indicates that its activity is the result of the 63-amino-acid protein it specifies. [ABSTRACT FROM AUTHOR]

The genetic element SLP1 exists in nature as a single DNA segment integrated into the genome of Streptomyces coelicolor. Upon mating with Streptomyces lividans, a closely related species, SLP1 undergoes precise excision from its chromosomal site and is transferred into the recipient where it integrates chromosomally. Previous work has shown that integration and excision involve site-specific recombination between a chromosomal site, attB, and a virtually identical sequence, attP, on SLP1. We demonstrate here by means of gene replacement that a tRNATyr sequence that overlaps part of the attB site of S. lividans is both biologically functional and essential for cell viability. The requirement for this tRNA gene has been used to stabilize the inheritance of a segrationally unstable plasmid in cells lacking a chromosomal attB site. The evolution of an essential DNA locus as an attachment site for a chromosomally integrating genetic element represents a novel mechanism of biological adaptation. [ABSTRACT FROM AUTHOR]

A protein containing a nucleotidyltransferase motif characteristic of poly(A) polymerases has been proposed to polyadenylate RNA in Streptomyces coelicolor (P. Bralley and G. H. Jones, Mol. Microbiol. 40:1155-1164, 2001). We show that this protein lacks poly(A) polymerase activity and is instead a tRNA nucleotidyltransferase that repairs CCA ends of tRNAs. In contrast, a Streptomyces coelicolor polynucleotide phosphorylase homologue that exhibits polyadenylation activity may account for the poly(A) tails found in this organism. [ABSTRACT FROM AUTHOR]

A tetR family transcriptional regulatory gene (SCO1712) was identified as a global antibiotic regulatory gene from a Streptomyces interspecies DNA microarray analysis. SCO1712 disruption in Streptomyces coelicolor not only upregulated antibiotic biosynthesis through pathway-specific regulators when a previously identified pleiotropic downregulatory wblA was expressed but also further stimulated antibiotic production in a wblA deletion mutant, implying that SCO1712 might encode a novel antibiotic downregulator. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the role of chaplins, a family of hydrophobic cell-surface proteins, in aerial mycelium formation in Streptomyces coelicolor. Identification of the chaplin family of cell surface-associated proteins; Effect of chp gene disruption on aerial hyphae formation and sporulation; Localization of the short chaplin proteins on the colony surface.

Using Streptomyces coelicolor microarrays to discover regulators of gene expression in other Streptomyces species, we identified wblA, a whiB-like gene encoding a putative transcription factor, as a down-regulator of doxorubicin biosynthesis in Streptomyces peucetius. Further analysis revealed that wblA functions pleiotropically to control antibiotic production and morphological differentiation in streptomycetes. Our results reveal a novel biological role for wblA and show the utility of interspecies microarray analysis for the investigation of streptomycete gene expression. [ABSTRACT FROM AUTHOR]