Multiple peptide synthetase gene clusters in Actinomycetes

Two oligonucleotide probes derived from conserved motifs in peptide synthet ases were hybridized with a cosmid Library of Planobispora rosea genomic DN A. Detailed characterization of the physical organization of the positive c osmids indicated the existence of at least eight unlinked contigs containin g multiple fragments that hybridized to both probes. Partial sequences of P CR products from the positive cosmids confirmed the existence of peptide sy nthetase genes. The combined results of hybridizations and physical mapping indicate that, in all likelihood, the isolated P. rosea contigs encode ove r 40 putative peptide synthetase modules. Similar results were obtained on screening a cosmid library of Actinoplanes teichomyceticus DNA. Furthermore , Southern hybridizations with several actinomycete strains, belonging to d ifferent genera, indicate that most strains contain multiple hybridizing ba nds - well in excess of the number expected from the structure of the oligo peptides produced by these strains. Even strains not reported to produce ol igopeptides gave clear positive signals when examined with the probes. Thes e results strongly suggest that actinomycetes devote a notable fraction of their genomes to the non-ribosomal synthesis of peptides, and that most str ains have the genetic potential to produce more oligopeptides than currentl y described.