Genetic and functional analysis of genes required for the post-modification of the polyketide antibiotic TA of Myxococcus xanthus

Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel 1 Department of Genetics, University of Leicester, Leicester LE1 7RH, UK 2 Author for correspondence: Eliora Z. Ron. Tel: +972 3 6409379. Fax: +972 3 6414138. e-mail: eliora{at}ccsg.tau.ac.il The antibiotic TA of Myxococcus xanthus is a complex macrocyclic polyketide, produced through successive condensations of acetate by a type I PKS (polyketide synthase) mechanism. The genes encoding TA biosynthesis are clustered on a 36 kb DNA fragment, which has been cloned and analysed. The chemical structure of TA and the mechanism by which it is synthesized indicate the need for several post-modification steps, which are introduced into the carbon chain of the polyketide to form the final bioactive molecule. These include the addition of several carbon atoms originating from acetate carbonyl, three C-methylations, O-methylation and a specific hydroxylation. This paper reports the analysis of five genes which are involved in the post-modification of TA. Their functional analysis, by specific gene disruption, suggests that they may be essential for the production of the active antibiotic. The characteristics and organization of the genes suggest that they may be involved in the addition of the carbon atoms which arise from acetate. Keywords: Myxococcus xanthus , polyketide synthase, acyl carrier protein, ß-ketoacyl ACP synthase III, antibiotic post-modification Abbreviations: ACP, acyl carrier protein; HMG, hydroxymethylglutaryl; KAS, ß-ketoacyl:ACP synthase; PKS, polyketide synthase The EMBL accession number for the sequence reported in this paper is AJ132503.