The
bldD
Gene of
Streptomyces coelicolor
A3(2): a Regulatory Gene Involved in Morphogenesis and Antibiotic Production
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abstract
ABSTRACT
The
bld
mutants of
Streptomyces coelicolor
A3(2) are blocked at the earliest stage of sporulation, the formation of aerial hyphae, and are pleiotropically defective in antibiotic production. Using a phage library of wild-type
S. coelicolor
DNA, we isolated a recombinant phage which restored both sporulation and antibiotic production to strains carrying the single known
bldD
mutation. Nucleotide sequence analysis of a 1.3-kb complementing subclone identified an open reading frame, designated
bldD
, encoding a translation product of 167 amino acid residues. Nucleotide sequence analysis of the
bldD
-containing fragment amplified from the chromosome of a
bldD
mutant strain revealed a point mutation changing a tyrosine residue at amino acid position 62 to a cysteine. Although a comparison of the BldD sequence to known proteins in the databases failed to show any strong similarities, analysis of the BldD sequence for secondary structural elements did reveal a putative helix-turn-helix, DNA recognition element near the C terminus of the protein. A comparison of
bldD
transcript levels in the
bldD+
and
bldD
mutant strains using both Northern blot analysis and S1 nuclease protection studies showed vast overexpression of
bldD
transcripts in the mutant, suggesting that BldD negatively regulates its own synthesis. High-resolution S1 nuclease mapping identified the transcription start point as a G residue 63 nucleotides upstream from the
bldD
start codon and 7 nucleotides downstream from −10 and −35 sequences resembling
E. coli
-like streptomycete promoters.
