Nodulated legumes receive their nitrogen via nitrogen-fixing rhizobia, which exist in a symbiotic relationship with the root system. In tropical legumes like French bean (Phaseolus vulgaris) or soybean (Glycine max), most of the fixed nitrogen is used for synthesis of the ureides allantoin and allantoic acid, the major long-distance transport forms of organic nitrogen in these species. The purpose of this investigation was to identify a ureide transporter that would allow us to further characterize the mechanisms regulating ureide partitioning in legume roots. A putative allantoin transporter (PvUPS1) was isolated from nodulated roots of French bean and was functionally characterized in an allantoin transport-deficient yeast mutant showing that PvUPS1 transports allantoin but also binds its precursors xanthine and uric acid. In beans, PvUPS1 was expressed throughout the plant body, with strongest expression in nodulated roots, source leaves, pods, and seed coats. In roots, PvUPS1 expression was dependent on the status of nodulation, with highest expression in nodules and roots of nodulated plants compared with non-nodulated roots supplied with ammonium nitrate or allantoin. In situ RNA hybridization localized PvUPS1 to the nodule endodermis and the endodermis and phloem of the nodule vasculature. These results strengthen our prediction that in bean nodules, PvUPS1 is involved in delivery of allantoin to the vascular bundle and loading into the nodule phloem.Availability of reduced nitrogen is an important determinant in the growth and development of plants. Although in most vascular plant species the major transport form of reduced/organic nitrogen is as amino acids (including amides), tropical and subtropical legumes like cowpea (Vigna unguiculata), soybean (Glycine max), and French bean (Phaseolus vulgaris) transport large amounts of the nitrogenous compounds called ureides. The dominant forms of ureides in these species are allantoin and allantoic acid (Pate et al., 1980). In legumes that are adapted to temperate climates (e.g. pea [Pisum sativum] and faba bean [Vicia faba]), the amides Gln and Asn take on the major transport function (Herridge et al., 1978;Schubert, 1986). Ureides can comprise up to 90% of the total nitrogen transported in the xylem of nitrogenfixing tropical legumes (Herridge et al., 1978;Pate et al., 1980) and can be stored in high amounts in the different plant organs (Matsumoto et al., 1977a;Streeter, 1979; Layzell and LaRue, 1982). In soybean, ureides have been found to be in concentrations of 20 or 10 mm in the stem tissue or xylem (Layzell and LaRue, 1982;Rainbird et al., 1984) and 94 mm in nodule exudate (Streeter, 1979). In leaves, total ureide concentrations varied from approximately 1 to 3 mm, but analyses of the various leaf cells have shown that ureides can reach concentration levels up to 59 mm in the paraveinal mesophyll (Matsumoto et al., 1977b;Thomas and Schrader, 1981; Costigan et al., 1987). Due to the high concentrations in the vascular system and in certain plant tiss...

Polyketomycin is a tetracyclic quinone glycoside produced by Streptomyces diastatochromogenes Tü6028. It shows cytotoxic and antibiotic activity, in particular against Gram-positive multi-drug-resistant strains (for example, MRSA). The polyketomycin biosynthetic gene cluster has been sequenced and characterised. Its identity was proven by inactivation of a alpha-ketoacyl synthase gene (pokP1) of the "minimal polyketide synthase II" system. In order to obtain valuable information about tailoring steps, we performed further gene-inactivation experiments. The generation of mutants with deletions in oxygenase genes (pokO1, pokO2, both in parallel and pokO4) and methyltransferase genes (pokMT1, pokMT2 and pokMT3) resulted in new polyketomycin derivatives, and provided information about the organisation of the biosynthetic pathway.

The oligosaccharide antibiotic avilamycin A is composed of a polyketide-derived dichloroisoeverninic acid moiety attached to a heptasaccharide chain consisting of six hexoses and one unusual pentose moiety. We describe the generation of mutant strains of the avilamycin producer defective in different sugar biosynthetic genes. Inactivation of two genes (aviD and aviE2) resulted in the breakdown of the avilamycin biosynthesis. In contrast, avilamycin production was not influenced in an aviP mutant. Inactivation of aviGT4 resulted in a mutant that accumulated a novel avilamycin derivative lacking the terminal eurekanate residue. Finally, AviE2 was expressed in Escherichia coli and the gene product was characterized biochemically. AviE2 was shown to convert UDP-D-glucuronic acid to UDP-D-xylose, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose. Here we report a UDP-D-glucuronic acid decarboxylase in actinomycetes.

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