Trans-acting regulation of antibiotic TA genes in Myxococcus xanthus

An unusual beta-ketoacyl:acyl carrier protein synthase and acyltransferase motifs in TaK, a putative protein required for biosynthesis of the antibiotic TA in Myxococcus xanthus

The antibiotic TA of Myxococcus xanthus is produced by a type-I polyketide synthase mechanism. Previous studies have indicated that TA genes are clustered within a 36-kb region. The chemical structure of TA indicates the need for several post-modification steps, which are introduced to form the final bioactive molecule. These include three C-methylations, an O-methylation and a specific hydroxylation. In this study, we describe the genetic analysis of taK, encoding a specific polyketide beta-ketoacyl:acyl carrier protein synthase, which contains an unusual beta-ketoacyl synthase and acyltransferase motifs and is likely to be involved in antibiotic TA post-modification. Functional analysis of this beta-ketoacyl:acyl carrier protein synthase by specific gene disruption suggests that it is essential for the production of an active TA molecule.

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

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.

A nonessential signal peptidase II (Lsp) of Myxococcus xanthus might be involved in biosynthesis of the polyketide antibiotic TA

Myxococcus xanthus is a gram-negative soil bacterium that produces the polyketide antibiotic TA. In this study, we describe the analysis of an M. xanthus gene which encodes a homologue of the prolipoprotein signal peptidase II (SPase II; lsp). Overexpression of the M. xanthus SPase II in Escherichia coli confers high levels of globomycin resistance, confirming its function as an SPase II. The M. xanthus gene encoding the lsp homologue is nonessential for growth, as determined by specific gene disruption. It has been mapped to the antibiotic TA gene cluster, and the disrupted mutants do not produce the antibiotic, indicating a probable involvement in TA production. These results suggest the existence of more than one SPase II protein in M. xanthus, where one is a system-specific SPase II (for TA biosynthesis).

Cloning and characterization of a Myxococcus xanthus cytochrome P-450 hydroxylase required for biosynthesis of the polyketide antibiotic TA

The antibiotic TA, a complex macrocyclic polyketide of Myxococcus xanthus, is produced, like many other polyketides, through successive condensations of acetate by a type I polyketide synthase (PKS) mechanism. The chemical structure of this antibiotic and the mechanism by which it is synthesized indicate the need for several post-modification steps, such as a specific hydroxylation at C-20. Previous studies have shown that several genes, essential for TA biosynthesis, are clustered in a region of at least 36kb, which was subsequently cloned and analyzed. In this study, we report the analysis of a DNA fragment, containing a specific cytochrome P-450 hydroxylase, presumably responsible for the sole non-PKS hydroxylation at position C-20. Functional analysis of the cytochrome P-450 hydroxylase gene through specific gene disruption confirms that it is essential for the production of an active TA molecule.

The first gene in the biosynthesis of the polyketide antibiotic TA of Myxococcus xanthus codes for a unique PKS module coupled to a peptide synthetase

The polyketide antibiotic TA is synthesized by the Gram negative bacterium Myxococcus xanthus in a multi-step process in which a unique glycine-derived molecule is used as a starter unit and elongated through the condensation of 11 acetate molecules by polyketide synthases (PKSs). Analysis of a 7.2 kb DNA fragment, encoding the protein that carries out the first condensation step, revealed that the fragment constitutes a single open reading frame, referred to as Ta1, which lacks the 5' and 3' ends and displays two regions of similarity to other proteins. The first 1020 amino acid residues at the N terminus of the polypeptide are similar to sequences of the large family of enzymes encoding peptide synthetases. They are followed by a second region displaying a high degree of similarity to type I PKS genes. The genetic analysis of this open reading frame is compatible with the proposed chemical structure of TA. The data indicate that the genes encoding TA have a modular gene organization, typical of a type I PKS system. The unusual feature of Ta1 is that the first PKS module of TA resides on the same polypeptide as the peptide synthetase functional unit.

A NusG-like transcription anti-terminator is involved in the biosynthesis of the polyketide antibiotic TA of Myxococcus xanthus

The antibiotic TA of Myxococcus xanthus is synthesized through a type I polyketide synthase mechanism. Previous studies have indicated that several genes essential for TA production are clustered within a 40-kb region and are transcriptionally co-regulated. In this study, we report the genetic analysis of the first gene in the TA gene cluster, identified as a NusG-like transcription anti-terminator. Functional analysis of this NusG-like anti-terminator gene by specific gene disruption confirms that it is essential for TA production but not for normal growth and development.