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T W Yu

Publications and source records attributed to T W Yu.

42 records · Page 3Linked to original sources
PubMed1994

The effect of various antioxidants and other modifying agents on oxygen-radical-generated DNA damage in human lymphocytes in the COMET assay.

The effects of antioxidants and various other modifying agents on oxygen-radical-generated DNA damage in human lymphocytes have been investigated using the COMET assay. Hydrogen peroxide (H2O2) and bleomycin (BLM) have produced clear dose-related responses. In 38 independent experiments, there was consistency between the two donors used in the study for the negative and positive control data. The endogenous antioxidant catalase abolished effects with H2O2, but only slightly affected the response with BLM. Superoxide dismutase did not alter the response with H2O2 and only slightly affected BLM. The exogenous antioxidant vitamin C produced a clear dose-related response on its own. In combination with H2O2, there were small protective effects at low doses and exacerbating effects at high doses, but these were within the inter-experimental variability range. Vitamin E (trolox) produced no effects with either H2O2 or BLM, or on its own. Silymarin protected against the effect due to H2O2. Other modifying agents such as apo-transferrin and deferoxamine mesylate produced a clear dose-related protection of effects due to BLM. This protection was less due to H2O2. In the presence of ferrous chloride, the effect due to BLM was exacerbated. In a small sample of 6 smokers and 6 non-smokers, responses from smokers approached borderline significance (P = 0.054) by comparison with non-smokers. These observations would suggest that the COMET assay is a useful tool for examining issues related to oxidative stress in human lymphocytes.

Adult↗
PubMed1994

Cloning, sequencing, and analysis of the griseusin polyketide synthase gene cluster from Streptomyces griseus.

A fragment of DNA was cloned from the Streptomyces griseus K-63 genome by using genes (act) for the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor as a probe. Sequencing of a 5.4-kb segment of the cloned DNA revealed a set of five gris open reading frames (ORFs), corresponding to the act PKS genes, in the following order: ORF1 for a ketosynthase, ORF2 for a chain length-determining factor, ORF3 for an acyl carrier protein, ORF5 for a ketoreductase, and ORF4 for a cyclase-dehydrase. Replacement of the gris genes with a marker gene in the S. griseus genome by using a single-stranded suicide vector propagated in Escherichia coli resulted in loss of the ability to produce griseusins A and B, showing that the five gris genes do indeed encode the type II griseusin PKS. These genes, encoding a PKS that is programmed differently from those for other aromatic PKSs so far available, will provide further valuable material for analysis of the programming mechanism by the construction and analysis of strains carrying hybrid PKS.

Amino Acid Sequence↗
PubMed1993

The conjugative plasmid SLP2 of Streptomyces lividans is a 50 kb linear molecule.

The SLP2 plasmid had previously been demonstrated genetically to exist in Streptomyces lividans by its ability to promote conjugation and to elicit 'pocks' on recipient (SLP2-) cultures, but it had not been physically detected. Using pulsed-field gel electrophoresis, a 50 kb linear DNA was isolated from SLP2+ but not SLP2- strains of S. lividans, and from Streptomyces coelicolor and Streptomyces parvulus strains to which SLP2 had been transferred by conjugation or transformation. We conclude that this linear DNA is SLP2. The terminal fragments of SLP2 were cloned. The determined sequences revealed a 44bp imperfect terminal inverted repeat. The terminal 12bp sequence of SLP2 was identical to those of two other Streptomyces linear plasmids, pSLA2 and pSCL, and similar to the terminal sequences of another Streptomyces linear plasmid, SCP1. The termini of SLP2 DNA were resistant to digestion by lambda exonuclease and ExoIII. A truncated (probably crippled) copy of Tn4811 is present on the plasmid. While the SLP2 plasmid exists as a free form in the host, a 15.7 kb sequence corresponding to the segment of SLP2 from Tn4811 to the right terminus is also present (at a copy number similar to the free form) elsewhere in the genome of S. lividans. Furthermore, SLP2 is partially homologous to a newly discovered 650 kb linear plasmid in S. parvulus.

Base Sequence↗
PubMed1993

The unstable melC operon of Streptomyces antibioticus is codeleted with a Tn4811-homologous locus.

The melC operon of Streptomyces antibioticus is unstable, undergoing frequent spontaneous deletions. All the delta melC mutants analyzed also lost 2-kb V1 DNA, which contained two open reading frames (ORFs) homologous to ORF4 (a putative oxidoreductase gene) and ORF5 (a putative AraC-type regulatory gene) of Tn4811. The two ORFs may constitute an accessory unit of a different transposon.

Amino Acid Sequence↗
PubMed1992

Discovery and characterization of a new transposable element, Tn4811, in Streptomyces lividans 66.

Transposition of a new 5.4-kb transposon, Tn4811, of Streptomyces lividans to the melC operon of Streptomyces antibioticus on plasmid pIJ702 was discovered. The nucleotide sequence of this copy of Tn4811, which contained an imperfect (9 of 11 bp) terminal inverted repeat, five putative Streptomyces coding sequences for an oxidoreductase and its transcription regulator, and three transposition-related proteins, was determined. SLP- strains of S. lividans contained one copy (A) of Tn4811, while SLP2+ strains contained an additional copy (B) on the SLP2 plasmid. The nucleotide sequences at three insertion junctions of Tn4811 were determined. Copy B lacked 41 bp from the left end. At the other five junctions the duplication of a putative 3-bp target sequence (TGA) was observed. A sequence of less than 3 kb homologous to Tn4811 was present in S. antibioticus. DNA homologous to Tn4811 was not detected in 14 other Streptomyces species.

Amino Acid Sequence↗