Different alleles of the response regulator gene bldM arrest Streptomyces coelicolor development at distinct stages

Mol Microbiol. 2000 Jun;36(6):1265-78. doi: 10.1046/j.1365-2958.2000.01977.x.


whiK was one of five new whi loci identified in a recent screen of NTG-induced whi mutants and was defined by three mutants, R273, R318 and R655. R273 and R318 produce long, tightly coiled aerial hyphae with frequent septation. In contrast, R655 shows a more severe phenotype; it produces straight, undifferentiated aerial hyphae with very rare short chains of spores. Subcloning and sequencing showed that whiK encodes a member of the FixJ subfamily of response regulators, with a C-terminal helix-turn-helix DNA-binding domain and an apparently typical N-terminal phosphorylation pocket. Unexpectedly, a constructed whiK null mutant failed to form aerial mycelium, showing that different alleles of this locus can arrest Streptomyces coelicolor development at very distinct stages. As a consequence of the null mutant phenotype, whiK was renamed bldM. The bldM null mutant fits into the extracellular signalling cascade proposed for S. coelicolor and is a member of the bldD extracellular complementation group. The three original NTG-induced mutations that defined the whiK/bldM locus each affected the putative phosphorylation pocket. The mutations in R273 and in R318 were the same, replacing a highly conserved glycine (G-62) with aspartate. The more severe mutant, R655, carried a C-7Y substitution adjacent to the highly conserved DD motif at positions 8-9. However, although bldM has all the highly conserved residues associated with the phosphorylation pocket of conventional response regulators, aspartate-54, the putative site of phosphorylation, is not required for bldM function. Constructed mutant alleles carrying either D-54N or D-54A substitutions complemented the bldM null mutant in single copy in trans, and strains carrying the D-54N or the D-54A substitution at the native chromosomal bldM locus sporulated normally. bldM was not phosphorylated in vitro with either of the small-molecule phosphodonors acetyl phosphate or carbamoyl phosphate under conditions in which a control response regulator protein, NtrC, was labelled efficiently.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles*
  • Amino Acid Sequence
  • Aspartic Acid / genetics
  • Aspartic Acid / metabolism
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Carbamyl Phosphate / metabolism
  • DNA, Bacterial
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism
  • Genes, Bacterial*
  • Helix-Turn-Helix Motifs*
  • Methylnitronitrosoguanidine / pharmacology
  • Molecular Sequence Data
  • Mutagenesis
  • Organophosphates / metabolism
  • Phosphorylation
  • Response Elements*
  • Streptomyces / drug effects
  • Streptomyces / genetics
  • Streptomyces / growth & development*
  • Streptomyces / ultrastructure
  • Transcription Factors*


  • Bacterial Proteins
  • BldD protein, Streptomyces coelicolor
  • BldM protein, Streptomyces coelicolor
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Organophosphates
  • Transcription Factors
  • Methylnitronitrosoguanidine
  • Aspartic Acid
  • acetyl phosphate
  • Carbamyl Phosphate

Associated data

  • GENBANK/AJ010601