Pactamycin is an aminocyclopentitol-derived natural product that has potent antibacterial and antitumor activities. Sequence analysis of an 86 kb continuous region of the chromosome from Streptomyces pactum ATCC 27456 revealed a gene cluster involved in the biosynthesis of pactamycin. Gene inactivation of the Fe-S radical SAM oxidoreductase (ptmC) and the glycosyltransferase (ptmJ), individually abrogated pactamycin biosynthesis; this confirmed the involvement of the ptm gene cluster in pactamycin biosynthesis. The polyketide synthase gene (ptmQ) was found to support 6-methylsalicylic acid (6-MSA) synthesis in a heterologous host, S. lividans T7. In vivo inactivation of ptmQ in S. pactum impaired pactamycin and pactamycate production but led to production of two new pactamycin analogues, de-6-MSA-pactamycin and de-6-MSA-pactamycate. The new compounds showed equivalent cytotoxic and antibacterial activities with the corresponding parent molecules and shed more light on the structure-activity relationship of pactamycin.

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