Urdamycin A, the principal product of Streptomyces fradiae Tu $ 2717, is an angucycline-type antibiotic and anticancer agent containing C-glycosidically linked D-olivose. To extend knowledge of the biosynthesis of urdamycin A the authors have cloned further parts of the urdamycin biosynthetic gene cluster. Three new ORFs (urdK, urdJ and urdO) were identified on a 335 kb fragment, and seven new ORFs (urdL, urdM, urdJ2, urdZ1, urdGT2, urdG and urdH) on an 805 kb fragment. The deduced products of these genes show similarities to transporters (urdJ and urdJ2), regulatory genes (urdK), reductases (urdO), cyclases (urdL) and deoxysugar biosynthetic genes (urdG, urdH and urdZ1). The product of urdM shows striking sequence similarity to oxygenases (N-terminal sequence) as well as reductases (C-terminal sequence), and the deduced amino acid sequence of urdGT2 resembles those of glycosyltransferases. To determine the function of urdM and urdGT2, targeted gene inactivation experiments were performed. The resulting urdM deletion mutant strains accumulated predominantly rabelomycin, indicating that UrdM is involved in oxygenation at position 12b of urdamycin A. A mutant in which urdGT2 had been deleted produced urdamycin I, urdamycin J and urdamycin K instead of urdamycin A. Urdamycins I, J and K are tetracyclic angucyclinones lacking a C-C connected deoxysugar moiety. Therefore UrdGT2 must catalyse the earliest glycosyltransfer step in the urdamycin biosynthetic pathway, the C-glycosyltransfer of one NDP-D-olivose.

A DNA fragment was cloned as cosmid purd8, which encodes a polyketide synthase involved in the production of the angucycline antibiotic urdamycin from Streptomyces fradiae Tü2717. Deletion of the polyketide synthase genes from the chromosome abolished urdamycin production. In addition, purd8 conferred urdamycin resistance on introduction into Streptomyces lividans TK24. Sequence analysis of 5.7 kb of purd8 revealed six open reading frames transcribed in the same direction. The deduced amino acid sequences of the six open reading frames strongly resemble proteins from known type II polyketide synthase gene clusters: a ketoacyl synthase, a chain length factor, an acyl carrier protein, a ketoreductase, a cyclase, and an oxygenase. Heterologous expression of the urdamycin genes encoding a ketoacyl synthase and a chain length factor in Streptomyces glaucescens tetracenomycin C-nonproducing mutants impaired in either the TcmK ketoacyl synthase or TcmL chain length factor resulted in the production of tetracenomycin C. Heterologous expression of a putative oxygenase gene from the urdamycin gene cluster in S. glaucescens GLA.O caused production of the hybrid antibiotic 6-hydroxy tetracenomycin C.

The transformation of α-Li3N to β-Li3N occurs at 600 MPa and room temperature. The reverse transformation, however, only begins to take place above 200°C under normal pressure. β-Li3N crystallizes as the Na3As structure type. This modification allows Li3N to be placed systematically in the structural series of alkali-metal compounds A3B involving elements of the nitrogen group (A = Li, Na, K, Rb, Cs; B = N, P, As, Sb, Bi). Since the phase transition occurs at relatively low pressure, the formation of small amounts of β-Li3N upon grinding with a mortar and pestle cannot be ruled out. Indeed, X-ray powder diffractions of α-Li3N always reveal the presence of small amounts of β-Li3N

No abstract

Genetically engineered hybrid strains, in which the genes of the urdamycin‐producer Streptomyce fradiae are combined with some of the biosynthetic genes of the elloramycin‐producer Streptomyces olivaceus or the genes of the tetracenomycin‐producer Streptomyces glaucescens, assemble novel hybrid antibiotics of the tetracenomycin type. The results prove that this combinatorial biosynthesis method may be a useful alternative for the production of new natural products which can then be screened.