Cloning, Sequencing, and Heterologous Expression of the <i>e</i><i>lmGHIJ </i>Genes Involved in the Biosynthesis of the Polyketide Antibiotic Elloramycin from <i>Streptomyces </i><i>o</i><i>livaceus</i> Tü2353

Abstract

Elloramycin A (1) belongs to a small family of naphthacenequinones characterized by a unique highly hydroxylated cyclohexenone moiety. A cosmid clone 16F4, harboring genes for the production of 1 from Streptomyces olivaceus Tü2353, has been previously isolated. DNA sequence analysis of a 3.2-kb fragment from 16F4 revealed four open reading frames--the elmGHIJ genes. Heterologous expressions of the elmGHI genes in either Escherichia coli or Streptomyces lividans, followed by biochemical characterizations of the ElmGHI proteins, established ElmG as tetracenomycin B2 oxygenase, ElmH as tetracenomycin F1 monooxygenase, and ElmI as tetracenomycin F2 cyclase. These results provide direct biochemical evidence for the hypothesis that the biosynthesis of 1 in S. olivaceus parallels that of tetracenomycin C (2) in Streptomyces glaucescens and support the notion that the biosynthesis of the highly hydroxylated cyclohexenone moiety in other polyketides most likely follows the same paradigm as the tetracenomycin B2 or A2 oxygenase.