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H L Yang

Publications and source records attributed to H L Yang.

At least 73 records · Page 4Linked to original sources
PubMed1984

Major coat protein and single-stranded DNA-binding protein of filamentous virus Pf3.

The region of the Pf3 virus genome encoding its major coat protein and its single-stranded DNA-binding protein is organized somewhat like the corresponding region of the fd (M13, f1) genome. Nevertheless, the major coat protein is unique among the major coat proteins of fd and the other filamentous phages studied in that it lacks a signal sequence and appears to be a direct translation product and in that it has fewer basic amino acid residues than its equivalent of DNA phosphates in the virion. These features are relevant to considerations of both protein insertion into membranes and DNA structure in filamentous viruses. The single-stranded DNA-binding protein also has a sequence that is different from the sequences of single-stranded DNA-binding proteins from other filamentous viruses.

Amino Acid Sequence↗
PubMed1983

Establishment of a physical and genetic map for bacteriophage PRD1.

DNA was isolated from the lipid-containing bacteriophage PRD1 and subjected to restriction endonuclease analysis. The total genome size is 14.7 kb. PRD1 DNA was resistant to cutting by fifteen restriction endonucleases with six base specificity. HaeII made thirty-seven cuts in the DNA, MboI made one cut, and MnlI made six cuts. DNA that was not treated with protease yielded two fewer fragments when treated with HaeII. Evidence is presented to indicate that the PRD1 DNA has protein at the ends of the DNA. The thirty-eight HaeII fragments were ordered using the ladder technique of Smith and Birnstiel (1976) on MboI and MnlI fragments of the genome. Clones of HaeII partial digests of PRD1 DNA in pBR322 were analyzed by HaeII digestion and were then assigned to specific regions of the genome by their HaeII fragment composition. A comparison of the marker rescue characteristics of the cloned DNA with the overall restriction fragment map generated a physical map of the genome. Some genes that have not been mapped because of a lack of mutants or leakiness at restrictive conditions were mapped by studying the in vitro protein synthesis of restriction endonuclease fragments.

Bacteriophages↗
PubMed1981

Further investigations of the capacity of polynuclear aromatic hydrocarbons to elicit atherosclerotic lesions.

Treatment of chickens for up to 20 wk with varying doses (0.1-10 mg/kg) of benzo[a]pyrene (BaP) or 7,12-dimethylbenz[a]anthracene (DMBA) resulted in significant increases in incidence and size of atherosclerotic lesions at the two higher doses utilized (1 and 10 mg/kg). Maximal lesion formation for birds treated chronically with BaP occurred at 1 mg/kg, while development of lesions in birds treated with DMBA was roughly linear over the dose range tested. The largest doses of BaP or DMBA (10 mg/kg for 20 wk) produced the highest percentage of chickens with detectable lesions (75 and 89%, respectively). Lower doses of BaP or DMBA resulted in a smaller percentage of birds (per group) with lesions, and the lowest dose (0.1 mg/kg) produced no statistical increase in lesion incidence. At approximately equimolar doses, DMBA appeared to be more potent than BaP in enhancing the development of lesions in the chickens. Administration of a single dose of BaP or DMBA followed by weekly doses of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) for 20 wk did not result in enhancement of lesion formation over the respective controls. Blood cholesterol was not significantly altered after treatment of chickens with DMBA, BaP, or TPA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

Cell-free coupled transcription-translation system for investigation of linear DNA segments.

Heretofore the DNA-directed coupled transcription-translation system, most useful in gene expression analysis, has been limited to the use of circular or long linear DNAs. Linear DNAs are degraded in this system by an exonucleolytic activity that can be eliminated by making the synthetic extracts from a suitable recB mutant of Escherichia coli. Using these extracts, we have examined the gene expression of a variety of linear DNAs. In particular, the complex pattern of expression of ribosomal protein genes and RNA polymerase genes in the rpoBC-rplLJ region has been analyzed by comparing the protein products obtained when using lambda rifd18 DNA with the product obtained when using the same DNA segmented with various restriction enzymes. The results obtained confirm the conclusions of others obtained by much more elaborate in vivo techniques. It seems highly likely that this cell-free system will have extensive applications in the area of analysis of gene expression.

Base Sequence↗
PubMed1979

Differential sensitivity of gene expression in vitro to inhibitors of DNA gyrase.

We have used the antibiotics coumermycin A1, novobiocin, and oxolinic acid, which are specific inhibitors of DNA gyrase, to study the coupled transcription and translation of several bacterial and plasmid genes in a DNA-directed cell-free system. The expression of different genes is reduced to different extents by inhibition of DNA gyrase activity. Among the genes tested, the lac operon, an rRNA gene, and the colicin gene of colicin E1 plasmid were found to be most sensitive, while the trp operon and some other genes in colicin E1 plasmid were relatively unaffected by the inhibitors. These results, together with earlier work on the transcription of circular DNA templates, indicate that DNA supercoiling can significantly enhance transcription from certain promoters.

Anti-Bacterial Agents↗
PubMed1976

In vitro synthesis and repression of argininosuccinase in Escherichia coli K12; partial purification of the arginine repressor.

Phi80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR+ strain but not by corresponding preparations from an argR- strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on beta-galactosidase synthesis.

Arginine↗
PubMed1976

Synthesis of an R plasmid protein associated with tetracycline resistance is negatively regulated.

Synthesis of proteins encoded by the R222 plasmid was observed in a DNA-directed cell-free system and the products were compared to those plasmid proteins synthesized in Escherichia coli minicells. A greater number of plasmid-specified proteins was detected in the in vitro system than in the minicell, suggesting the presence of control factors for plasmid gene expression in the minicell. Synthesis of a newly detected plasmid protein (TET protein) is induced by tetracycline in minicells containing tetracycline-resistant plasmids, including R222, and this induced synthesis correlates with induced host resistance to the drug. This TET protein was synthesized in vitro from R222 DNA in the absence of tetracycline, indicating that no positive regulatory role for tetracycline is required for the protein's synthesis. TET proteon synthesis was inhibited in vitro when cell-free extracts prepared from cells containing the R222 plasmid were used.

Bacterial Proteins↗
PubMed1975

Effects of bacteriophage T4-induced modification of Escherichia coli RNA polymerase on gene expression in vitro.

After T4 bacteriophage infection of E. coli a complex series of events take place in the bacterium, including gross inhibition of host transcription and discrete changes in the classes of the genes of T4 that are transcribed. Accompanying these changes in the pattern of transcription one finds T4-induced changes in the RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase). The effects of modified polymerase on transcription can be advantageously analyzed in a DNA-directed cell-free system for protein synthesis. In this system gene activity is measured indirectly by the amounts and types of proteins sythesized. In the DNA-directed cell-free system this modified polymerase, like normal polymerase, transcribes T4 DNA with a high efficiency but transcribes bacteriophage lambda and host DNA very poorly. Polymerase reconstruction experiments show that modification of the alpha subunit of the RNA polymerase is sufficient for inhibition of host transcription. Host transcription is also inhibited in vitro by T4 DNA. This latter type of inhibition is presumed to involve competition between host DNA and T4 DNA for some factor essential for transcription. The T4-modified polymerase transcribes from T4 DNA many of the same genes as normal unmodified polymerase; it also shows a capability for transcribing certain "non-early" T4 genes which is enhanced in the presence of protein-containing extracts from T4-infected cells.

Coliphages↗
PubMed1975

Effects of guanosine tetraphosphate on cell-free synthesis of Escherichia coli ribosomal RNA and other gene products.

A cell-free system derived from E. coli is described in which mature-sized 16S and 23S ribosomal RNAs (rRNA) are synthesized at a high relative rate, comprising 17-25% of the total transcription. The addition of guanosine tetraphosphate (ppGpp) to this system results in up to a 5-fold selective inhibition of rRNA accumulation. This effect is exerted at the level of synthesis rather than degradation. It is concluded that ppGpp, which is produced in large amounts by E. coli during amino-acid deprivation, could mediate the decrease in rRNA synthesis that accompanies such deprivation. The expression of other genes has also been investigated. No selective reduction of transfer RNA synthesis by ppGpp is observed. The trp and lac operons are found to be stimulated at the transcriptional level by the presence of this nucleotide. It is hypothesized that ppGpp interacts with the RNA polymerase in such a manner as to alter the affinity of the enzyme for promoters in an operon-specific fashion.

Cell-Free System↗
PubMed1974

Effects of guanosine tetraphosphate, guanosine pentaphosphate, and beta-gamma methylenyl-guanosine pentaphosphate on gene expression of Escherichia coli in vitro.

The effects of guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), both produced by E. coli, were measured on the activities of several genes in a cell-free system. Gene activity is measured as gene-directed synthesis of biochemically competent protein or transfer RNA. Both ppGpp and pppGpp stimulated the activities of the ara, lac, and trp operons and inhibited the arg operon. Production of transfer-RNA(Tyr) was unaffected by moderate levels of either ppGpp or pppGpp and only slightly inhibited at higher levels of ppGpp. Since the cell-free reaction mixtures hydrolyze pppGpp to ppGpp, we performed similar studies with a hydrolysis-resistant analog of pppGpp, the beta-gamma methylenyl derivative (pcppGpp). In general, pcppGpp shows the same inhibitory potency as pppGpp for the arg operon, but lacks the stimulatory effects on the ara, lac, and trp operons. This result suggests that the stimulation of these gene activities is specific for ppGpp.Under similar conditions, pppGpp and ppGpp show a slight inhibitory effect on the messenger-directed synthesis of beta-galactosidase and no effect on the messenger-directed synthesis of MS2 viral-coat protein. These observations, together with the fact that in the same system these nucleotides affect coupled transcription and translation, lead us to surmise that the activities of pppGpp and ppGpp are exerted at the level of RNA polymerase activity.

Acetamides↗
PubMed1974

Genetic analysis of the leucine region in Escherichia coli B-r: gene-enzyme assignments.

Genetic mapping by transduction and conjugation using F(-) and F' strains carrying either point mutations in the l-arabinose or leucine regions or ara-leu fusion-deletion mutations has resulted in a detailed genetic map of the arabinose-leucine region of Escherichia coli B/r. These studies have identified four genes in the leucine region having the same order as found in Salmonella typhimurium: ara... leuDCBA.

Acyltransferases↗
PubMedDate not supplied

Iatrogenic hyperadrenocorticism in 28 dogs.

Twenty-eight dogs with iatrogenic hyperadrenocorticism were studied. The most common clinical signs were cutaneous lesions (27/28), polydipsia (21/28), polyuria (19/28), and lethargy (16/28). The most predominant findings on biochemical profile were elevated alkaline phosphatase (ALP, 15/28) and alanine transferase (ALT, 14/28); hypercholesterolemia (14/28); elevated aspartate transferase (AST, 12/28); and elevated triglycerides (12/18). Baseline cortisol levels of all 28 dogs were at the lower end of the reference range and exhibited suppressed or no response to adrenocorticotropic hormone (ACTH) stimulation. The mean time for each dog to show initial improvement of clinical signs after corticosteroid withdrawal was six weeks, with another mean time of 12 weeks to demonstrate complete remission.

Adrenal Cortex↗