Although phenylpropanoids and flavonoids are common plant natural products, these major classes of biologically active secondary metabolites are largely absent from bacteria. The ubiquitous plant enzymes phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) are key biosynthetic catalysts in phenylpropanoid and flavonoid assembly, respectively. Until recently, few bacterial counterparts were known, thus reflecting the dearth of these plant natural products in bacteria. This review highlights our progress on the biochemical and genetic characterization of recently identified streptomycete biosynthetic pathways to benzoic acid and type III polyketide synthase (PKS)-derived products. The sediment-derived bacterium "Streptomyces maritimus" produces benzoyl-CoA in a plant-like manner from phenylalanine involving a PAL-mediated reaction through cinnamic acid during the biosynthesis of the polyketide antibiotic enterocin. All but one of the genes encoding benzoyl-CoA biosynthesis in "S. maritimus" have been cloned, sequenced, and inactivated, providing a model for benzoate biosynthesis not only in this bacterium, but in plants where benzoic acid is an important constituent of many products. The recent discovery that bacteria harbor homodimeric PKSs belonging to the plant CHS superfamily of condensing enzymes has further linked the biosynthetic capabilities of plants and bacteria. A bioinformatics approach led to the prediction that the model actinomycete Streptomyces coelicolor A3(2) contains up to three type III PKSs. Biochemical analysis of one of the recombinant type III PKSs from S. coelicolor demonstrated activity as a 1,3,6,8-tetrahydroxynaphthalene synthase (THNS). A homology model of THNS based upon the known three-dimensional structure of CHS was constructed to explore the structural and mechanistic details of this new subclass of bacterial PKSs.

Sequence analysis of the metabolically rich 8.7-Mbp genome of the model actinomycete Streptomyces coelicolor A3(2) revealed three genes encoding predicted type III polyketide synthases (PKSs). We report the inactivation, expression, and characterization of the type III PKS homologous SCO1206 gene product as 1,3,6,8-tetrahydroxynaphthalene synthase (THNS). Incubation of recombinant THNS with malonyl-CoA showed THN production, as demonstrated by UV and HPLC analyses. The K(m) value for malonyl-CoA and the k(cat) value for THN synthesis were determined spectrophotometrically to be 3.58+/-0.85 micro M and 0.48+/-0.03 min(-1), respectively. The C-terminal region of S. coelicolor THNS, which is longer than most other bacterial and plant type III PKSs, was shortened by 25 amino acid residues and the resulting mutant was shown to be slightly more active (K(m)=1.97+/-0.19 micro M, k(cat)=0.75+/-0.04 min(-1)) than the wild-type enzyme.

No abstract

No abstract

This study investigated telomeric array organization of diverse chicken genotypes utilizing in vivo and in vitro cells having phenotypes with different proliferation potencies. Our experimental objective was to characterize the extent and nature of array variation present to explore the hypothesis that mega-telomeres are a universal and fixed feature of chicken genotypes. Four different genotypes were studied including normal (UCD 001, USDA-ADOL Line 0), immortalized (DF-1), and transformed (DT40) cells. Both cytogenetic and molecular approaches were utilized to develop an integrated view of telomeric array organization. It was determined that significant variation exists within and among chicken genotypes for chromosome-specific telomeric array organization and total genomictelomeric sequence content. Although there was variation for mega-telomere number and distribution, two mega-telomere loci were in common among chicken genetic lines (GGA 9 and GGA W). The DF-1 cell line was discovered to maintain a complex derivative karyotype involving chromosome fusions in the homozygous and heterozygous condition. Also, the DF-1 cell line was found to contain the greatest amount of telomeric sequence per genome (17%) as compared to UCD 001 (5%) and DT40 (1.2%). The chicken is an excellent model for studying unique and universal features of vertebrate telomere biology, and characterization of the telomere length variation among genotypes will be useful in the exploration of mechanisms controlling telomere length maintenance in different cell types having unique phenotypes.