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Saframycin M x l is a DNA-binding antibiotic and antitumour agent produced by Myxococcus xanthus. It is a heterocyclic quinone, thought to be synthesized via the linear pepide intermediate AlaGlyTyrTyr. Analysis of 14-1 kb DNA sequence involved in saframycin production revealed genes for two large multifunctional peptide synthetases of 1770 and 2605 amino acids, respectively, and a putative 0-methyltransferase of 220 amino acids. The three ORFs read in the same direction and are separated by short non-translated gaps of 4 4 and 49 bp. The peptide synthetases contain two amino-acid-activating domains each. The first domain lacks two of the most conserved 'core' sequences, and the last domain is followed by a putative reductase functionality, not previously seen in peptide synthetases. Complementation tests showed that antibiotic-nonproducing mutant strains lacking one of the peptide synthetases secrete a substrate, presumably a modified amino acid precursor, that can be used by 0-methyltransferase-def icient mutant strains to synthesize saframycin M x l .

The gene cluster for the biosynthesis of the heterocyclic quinone antibiotic saframycin Mxl of Myxococcus xanthus DM5W15 was inactivated and tagged by TnS insertions. The tagged genes were cloned in Escherichia coli and used to select overlapping cosmid clones spanning 58 kb of the M. xanthus genome.Gene disruption experiments defined a 2 18 kb contiguous DNA region involved in saf ramycin biosynthesis. Sequencing of part of this region revealed a large ORF containing two 600-amino-acid domains with similarity to peptide synthetase aminolacid-activating sequences, suggesting that saframycin M x l is synthesized by a nonribosomal multienzyme complex, similar to other bioactive peptides.

Stigmatella aurantiaca is a prokaryotic organism that undergoes a multicellular cycle of development resulting in the formation of a fruiting body. For analyzing this process, mutants defective in fruiting body formation have been induced by transposon mutagenesis using a Tn5-derived transposon. About 800 bp upstream of the transposon insertion of mutant AP182 which inactivates a gene (fbfB) involved in fruiting, a further gene (fbfA) needed for fruiting body formation was detected. Inactivation of fbfA leads to mutants which form only nonstructured clumps instead of the wild-type fruiting body. The mutant phenotype of fbfA mutants can be partially suppressed by mixing the mutant cells with cells of some independent mutants defective in fruiting body formation. The fbfA gene is transcribed after 8 h of development as determined by measuring the induction of ␤-galactosidase activity of a fbfA-⌬trp-lacZ fusion gene and by Northern (RNA) analysis using an insertion encoding a stable mRNA. The predicted polypeptide FbfA shows a homology of about 30% to NodC of rhizobia, an N-acetylglucosamine-transferase which is involved in the synthesis of the sugar backbone of lipooligosaccharides. These induce the formation of the root nodules in the Papilionaceae. Besides the predicted molecular mass of 45.5 kDa, the hydropathy profile reveals a structural relationship to the NodC polypeptide.Multicellular morphogenesis is a feature of many eukaryotes and of a group of social prokaryotes, the myxobacteria. They are gram-negative soil bacteria growing on insoluble organic substrates such as decaying wood or leaves. Myxobacteria interact with each other, forming swarms. The cells move by gliding and secrete slime containing lytic enzymes that degrade biopolymers. Upon starvation, cells glide into aggregation centers from which arise the fruiting bodies, structures with a defined species-specific morphology and diverse complexity, harboring spores (10, 44). As in eukaryotic multicellular morphogenesis, direct cell-cell interaction and communication as well as positional signalling are predicted to play an important role in fruiting body formation of myxobacteria (8,21,23). Stigmatella aurantiaca belongs to the order of the myxobacteria. The fruiting body of S. aurantiaca is differentiated into a stalk and several delicate pedicels bearing a sporangiole at the top which contain between 10 4 and 10 5 myxospores. The morphological changes during development occur in a defined, temporal sequence, and in S. aurantiaca, the whole process takes about 24 h. Thus S. aurantiaca provides a simple and well-suited model system to study the development of morphological structures. Sporulation of vegetative cells may be induced independently from fruiting body formation by using indole and some of its derivatives (12).To detect genes involved in the morphogenesis of the S. aurantiaca fruiting body, transposon mutants defective in fruiting body formation have been induced with the promotor probe transposon Tn5lacZ (36). The fbfA gene which has be...