g., [14–17]). The best studied multiple pathway-specific BMN 673 regulatory cascade involves remarkably five

regulatory genes in tylosin biosynthetic gene cluster of S. fradiae, and a model for their regulation has been proposed [14, 18–23]. Deciphering the complexity of these pathway-specific regulatory networks is of great interest not only for better understanding of the antibiotic regulatory mechanism, but also for providing new strategy for targeted genetic engineering of antibiotic producing strains. C-1027 nonpeptidic chromophore is a structure of an enediyne core, a deoxy aminosugar, a β-amino acid and a benzoxazolinate (Fig. 1) [7]. The biosynthetic gene cluster for C-1027, which is the first cloned enediyne gene cluster, contains a total of 56 open reading frames (ORFs) in a region LCZ696 of 75 kbp [24, 25]. Bioinformatic analysis SCH772984 order and biochemical studies revealed a distinct iterative type I enediyne polyketide synthase (SgcE) and provided a convergent biosynthetic strategy for C-1027 from four biosynthetic building blocks [25]. Further cloning and characterization of biosynthetic gene clusters for four other enediynes (CAL [26], NCS [27], maduropeptin (MDP) [28] and dynemicin [29]) confirmed the unifying paradigm for enediyne biogenesis. In accordance with the complexity of the biosynthetic process,

there are no fewer than three ORFs annotated as transcriptional regulators in each known enediyne antibiotic biosynthetic cluster. At least three putative regulatory genes (sgcR1, sgcR2 and sgcR3) associated with the C-1027 biosynthetic gene cluster of S. globisporus C-1027 were annotated in the earlier work by sequence analysis [25]. Furthermore, the biosynthetic gene clusters for two 9-membered enediynes produced by streptomycetes (C-1027 and NCS) show high similarity in the organization

of genes around these regulatory genes (Fig. 2A). Despite chromophore structural uniqueness, all homologues of three genes are located adjacent to the genes of enediyne PKSs (sgcE and ncsE) and the tailoring enzymes (E1 to E11), which are responsible for the biosynthesis of enediyne core. However, almost no cognitional knowledge was acquired about the transcriptional regulation of enediyne antibiotic production prior to the present work. Figure 1 Structure of C-1027 chromophore. Figure 2 Comparison of two 9-membered enediyne (C-1027 and Oxalosuccinic acid NCS) biosynthetic gene clusters around the genes of enediyne PKS ( sgcE and ncsE ) (A) and amino acid sequence alignment for SgcR3 (B). A, Open reading frames are indicated by arrows. Homologue genes of regulatory sgcR1, sgcR2 and sgcR3 identified by sequence analysis are shown in grey or black. Genes outside of the clusters are marked by broken line arrows. B, The multialignment of S. globisporus C-1027 SgcR3, S. carzinostaticus ATCC 15944 NscR7 and S. fradiae TylR. Identical residues are highlighted in black and similar residues are shaded.