Study of the bldG locus suggests that an anti-anti-sigma factor and an anti-sigma factor may be involved in Streptomyces coelicolor antibiotic production and sporulation The GenBank accession numbers for the sequences reported in this paper are AF134889 and AL035636

Abstract

A cloned 25 kb DNA fragment that can restore antibiotic production and sporulation to a bldG mutant encodes a 113 aa protein showing similarity to a family of anti-anti-sigma factors from Bacillus and Staphylococcus ; and the deduced product of a closely spaced downstream ORF, designated ORF3, shows similarity to cognate anti-sigma factors. The homologues in Bacillus regulate the activity of sporulation-and stress-response-specific sigma factors. However, there is no sigma factor gene near bldG and ORF3. bldG is transcribed both as a monocistronic and a polycistronic mRNA, the latter including the downstream ORF3 gene. The two transcripts were present at all time points during growth and both were upregulated when aerial mycelium and pigmented antibiotics were seen. At all time points, the monocistronic bldG transcript was two-to threefold more abundant than the polycistronic transcript. Mapping of the mRNA 5' ends indicated that bldG transcription is initiated from two transcription start sites located 82 and 123 bp upstream of the bldG translation start. A constructed bldG null mutant had the same phenotype as previously isolated bldG point mutations, some of which were shown to have potentially significant base changes within bldG. When compared to the wild-type strain, the null mutant showed no differences in the levels of transcription from the two bldG promoters. These results suggest that bldG is not involved in autoregulation.

RNA Polymerase Sigma Factor That Blocks Morphological Differentiation by Streptomyces coelicolor

“…A relatively small number of genes involved in this developmental pathway, the bld genes, have been characterized (2,4,11,19,24,26,31), and only recently have relationships between the activities of certain bld gene products been established (2,10). Here we describe the identification and initial characterization of a new gene, rsuA, which is indirectly required for the formation of aerial hyphae, as well as for the appropriate timing of pigmented antibiotic production.…”

“…Presumably, and opposite to the other cases we have considered, a bldG mutation blocks aerial mycelium formation by preventing the activation of a sigma factor that is required for development. However, a cognate sigma factor for the bldG system, if it exists, is unknown (4).…”

“…These mutants exhibit a bald (bld) phenotype; the surface of mutant colonies remains smooth and does not accumulate the hairlike aerial hyphae. Whereas the corresponding bld genes have been identified from some of these mutant strains (2,4,11,19,24,26,31), it is clear that many genes that influence aerial mycelium formation remain to be uncovered (27). A striking property of bld mutants is their capacity to be rescued by extracellular complementation, a phenomenon that has been interpreted to indicate the existence of signaling molecules that help to regulate aerial mycelium formation under certain conditions (26,32).…”

Carbon source regulation of antibiotic production

“…114 With regard to bldG, it has been proposed that this gene encodes a putative anti-anti-sigma factor that might control transcription of both aerial mycelia formation and antibiotic formation. 120 Using transposon mutagenesis, Chouayekh et al 121 isolated S. lividans TK24 mutants the a-amylase expression of which was resistant to glucose catabolite repression. Mutant characterization showed interruption of the sblA gene (equivalent to SCO0479 of S. coelicolor).…”

The Anti-Anti-Sigma Factor BldG Is Involved in Activation of the Stress Response Sigma Factor σ H in Streptomyces coelicolor A3(2)

“…One of the other homologues of B. subtilis anti-anti-sigma factor RsbV encoded by the bldG gene (SCO3549) has been shown to have a pleiotropic function in controlling both antibiotic production and differentiation in S. coelicolor A3(2) (7, 9). Downstream of bldG is the gene apgA (SCO3548) that encodes a homologue of B. subtilis anti-sigma factor RsbW, and these two genes are cotranscribed (7). BldG has been shown to interact with ApgA as a part of a regulatory system to control both antibiotic production and differentiation in S. coelicolor, suggesting that they form a partner-switching pair; however, no target sigma factor has been identified for this system (43).…”