Temperature Areas of Local Inelasticity in Polyoxymethylene.

The spectra of internal friction and temperature dependencies of the frequency of a free-damped oscillation process excited in the specimens of an amorphous-crystalline copolymer of polyoxymethylene with the co-monomer trioxane (POM-C) with a degree of crystallinity ~60% in the temperature range from -150 °C to +170 °C has been studied. It has been established that the spectra of internal friction show five local dissipative processes of varying intensity, manifested in different temperature ranges of the spectrum. An anomalous decrease in the frequency of the oscillatory process was detected in the temperature ranges where the most intense dissipative losses appear on the spectrum of internal friction.

The calicheamicin gene cluster and its iterative type I enediyne PKS.

The enediynes exemplify nature's ingenuity. We have cloned and characterized the biosynthetic locus coding for perhaps the most notorious member of the nonchromoprotein enediyne family, calicheamicin. This gene cluster contains an unusual polyketide synthase (PKS) that is demonstrated to be essential for enediyne biosynthesis.

Insights about the biosynthesis of the avermectin deoxysugar L-oleandrose through heterologous expression of Streptomyces avermitilis deoxysugar genes in Streptomyces lividans.

Background: The avermectins, produced by Streptomyces avermitilis, are potent anthelminthic agents with a polyketide-derived macrolide skeleton linked to a disaccharide composed of two alpha-linked L-oleandrose units. Eight contiguous genes, avrBCDEFGHI (also called aveBI-BVIII), are located within the avermectin-producing gene cluster and have previously been mapped to the biosynthesis and attachment of thymidinediphospho-oleandrose to the avermectin aglycone. This gene cassette provides a convenient way to study the biosynthesis of 2,6-dideoxysugars, namely that of L-oleandrose, and to explore ways to alter the biosynthesis and structures of the avermectins by combinatorial biosynthesis.

A two-plasmid system for the glycosylation of polyketide antibiotics: bioconversion of epsilon-rhodomycinone to rhodomycin D.

Background: The biological activity of many microbial products requires the presence of one or more deoxysugar molecules attached to agylcone. This is especially prevalent among polyketides and is an important reason that the antitumor anthracycline antibiotics are avid DNA-binding drugs. The ability to make different deoxyaminosugars and attach them to the same or different aglycones in vivo would facilitate the synthesis of new anthracyclines and the quest for antitumor drugs.

Doxorubicin overproduction in Streptomyces peucetius: cloning and characterization of the dnrU ketoreductase and dnrV genes and the doxA cytochrome P-450 hydroxylase gene.

Doxorubicin-overproducing strains of Streptomyces peucetius ATCC 29050 can be obtained through manipulation of the genes in the region of the doxorubicin (DXR) gene cluster that contains dpsH, the dpsG polyketide synthase gene, the putative dnrU ketoreductase gene, dnrV, and the doxA cytochrome P-450 gene. These five genes were characterized by sequence analysis, and the effects of replacing dnrU, dnrV, doxA, or dpsH with mutant alleles and of doxA overexpression on the production of the principal anthracycline metabolites of S. peucetius were studied.