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The main flavonoids were isolated from three selected onion cultivars. Three phenolic compounds were obtained by reverse-phase HPLC, and their structures were elucidated by multiple NMR measurements. There were two known compounds, quercetin and quercetin 3′-O-β-d-glucopyranoside (Q3′G), and one novel compound, quercetin 3-O-β-d-glucopyranoside-(4→1)-β-d-glucopyranoside (Q3M), which was identified in onion for the first time. These flavonoids were found to be more abundant in the onion peel than in the flesh or core. Their antioxidative activities were tested using the DPPH method, and their antiaging activities were evaluated using a Caenorhabditis eleganslifespan assay. No direct correlation was found between antioxidative activity and antiaging activity. Quercetin showed the highest antioxidative activity, whereas Q3M showed the strongest antiaging activity among these flavonoids, which might be related to its high hydrophilicity.

TheletA(ccdA) andletD(ccdB) genes of the F plasmid, located just outside the sequence essential for replication, contribute to stable maintenance of the plasmid inEscherichia colicells. TheletDgene product acts to inhibit partitioning of chromosomal DNA and cell division by inhibiting DNA gyrase activity, whereas theletAgene product acts to reverse the inhibitory activity of theletDgene product. To identify the host factor(s) involved in this process, we analyzed the mutants that escapedletDexpression and their suppressor, and found that the threeE. coligenestldD,tldEandzfiAparticipate in the process, in addition to thegroEgenes we reported previously. ThetldDandtldEmutations made cells tolerant forletDexpression, as didgroESmutations, while the mutation in thezfiAgene madetldD,tldEandgroESmutants LetD sensitive. We hypothesize that these gene products are factors that modulate activity of DNA gyrase along with theletDgene product; thezfiAgene product acts to inhibit interaction between the LetD protein and the A subunit of DNA gyrase, while thetldD,tldEandgroEgene products act to suppress the inhibitory activity of thezfiAgene product. ThetldD,tldE, andzfiAgenes are located at 70.4, 96.0 and 58.2 minutes on theE. colichromosome, respectively, and code for proteins with relative molecular masses of 51,000, 48,000 and 6800, respectively.tldDis a novel gene, but thetldEandzfiAgenes proved to be thepmbAgene (production of Microcin B17) and thecsrAgene (carbon storage regulator), respectively.