Analysis of the tunicamycin biosynthetic gene cluster of Streptomyces chartreusis reveals new insights into tunicamycin production and immunity
The tunicamycin biosynthetic gene cluster of Streptomyces chartreusis consists of 14 genes (tunA-N) with a high degree of apparent translational coupling. Transcriptional analysis revealed that all of these genes are likely to be transcribed as a single operon from two promoters, tunp1 and tunp2. In frame deletion analysis revealed that just six of these genes (tunABCDEH) are essential for tunicamycin production in the heterologous host Streptomyces coelicolor, while five (tunFGKLN) with likely counterparts in primary metabolism are not necessary, but presumably ensure efficient production of the antibiotic at the onset of tunicamycin biosynthesis. Three genes are implicated in immunity; tunIJ, which encode a two component ABC transporter presumably required for export of the antibiotic, and tunM, which encodes a putative SAM-dependent methyltransferase. Expression of tunIJ or tunM in S. coelicolor conferred resistance to exogenous tunicamycin. The results presented here provide new insights into tunicamycin biosynthesis and immunity.