THE BLDD GENE OF STREPTOMYCES-COELICOLOR A3(2) - A REGULATORY GENE INVOLVED IN MORPHOGENESIS AND ANTIBIOTIC PRODUCTION

The bid mutants of Streptomyces coelicolor A3(2) are blocked at the ea rliest stage of sporulation, the formation of aerial hyphae, and are p leiotropically defective in antibiotic production. Using a phage libra ry of wild-type S. coelicolor DNA, se isolated a recombinant phage whi ch restored both sporulation and antibiotic production to strains carr ying the single known bldD mutation. Nucleotide sequence analysis of a 1.3-kb complementing subclone identified an open reading frame, desig nated bldD, encoding a translation product of 167 amino acid residues. Nucleotide sequence analysis of the bldD-containing fragment amplifie d from the chromosome of a bldD mutant strain revealed a point mutatio n changing a tyrosine residue at amino acid position 62 to a cysteine. Although a comparison of the BldD sequence to known proteins in the d atabases 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 protei n. A comparison of bldD transcript levels in the bldD(+) and bldD muta nt strains using both Northern blot analysis and SI nuclease protectio n studies showed vast overexpression of bldD transcripts in the mutant , suggesting that BldD negatively regulates its own synthesis. High-re solution 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.