PubMed Health⌕ Search

Biomedical subjects

B H Nicholson

Publications and source records attributed to B H Nicholson.

29 records · Page 2Linked to original sources
PubMed1971

Location of aromatic amino acids and belix content in Escherichia coli ribonucleic acid polymerase.

1. The perturbing effect of glycerol on the direct spectrum of Escherichia coli DNA-dependent RNA polymerase has been studied. 2. By comparison with model compounds and with the unfolded polymerase in 3.8m-urea it was possible to determine the ratio of tyrosine and tryptophan residues present. On reduction of the urea-treated enzyme with 2-mercaptoethanol, no further change in the difference spectrum occurred. 3. The amino acid composition of the enzyme is given. 4. In the intact protein approx. 30% of the tryptophan and 54% of the tyrosine residues were exposed. In conjunction with the extinction value and molecular weight this corresponded to 7 tryptophan residues and 57 tyrosine residues on the surface and 16 tryptophan residues and 48 tyrosine residues ;buried'. 5. The optical rotatory dispersion of the enzyme was unaffected by 20% glycerol. 6. The helix content calculated from Moffit plots over 560-300nm was 13%, and from the 233nm trough 13%.

Amino Acids↗
PubMed1969

The interaction of aflatoxin B1 with polynucleotides and its effect on ribonucleic acid polymerase.

1. The interaction of aflatoxin B(1) with different polynucleotides was studied spectrophotometrically. Equations were derived that enable the degree of binding to be determined without first determining the extinction coefficient of the bound form. 2. The interaction with calf thymus DNA obeys first-order relationships with an association constant of 0.40mm(-1), but there is some evidence for a secondary binding process from results obtained at 390nm. 3. The spectral shifts decreased in the order polyadenylic acid+polyuridylic acid>DNA>polyadenylic acid>polyadenylic acid+polyinosinic acid. Polycytidylic acid, polyuridylic acid, polyinosinic acid (both single- and triple-stranded), AMP, CMP, GMP and UMP did not interact with aflatoxin. It was concluded that there is a requirement for the amino group of adenine (or possibly guanine) for binding of aflatoxin to polynucleotides to occur. 4. Binding is reversed by increasing ionic strength, and by Mn(2+) and Mg(2+) in the concentration range studied (0-5mm). The effect of the Mn(2+) or Mg(2+) was far greater than would be expected on the basis of their ionic strength. With both the bivalent cations and sodium chloride the reversal is greatest with double-stranded polynucleotides. 5. Inhibition in vitro of the DNA-dependent RNA polymerase of Escherichia coli by aflatoxin B(1) was detected only in the absence of Mg(2+) and at concentrations of Mn(2+) below the optimum for RNA synthesis in vitro. 6. The degree of inhibition (maximally 30%) was dependent on the concentration of Mn(2+) and decreased during incubation.

Adenine Nucleotides↗
PubMed1967

The effects of gamma-irradiation on the priming by deoxyribonucleohistone of ribonucleic acid polymerase.

1. The effect of gamma-irradiation of solutions of DNA and deoxyribonucleohistone (DNH) on their ability to prime the synthesis of RNA by DNA-dependent RNA polymerase has been studied. 2. The priming ability of both DNA and DNH decreased continuously with increasing radiation dose, but more rapidly with DNH. 3. These decreases have been compared with decreases in molecular weight and with the breakdown of the specific hydrogen-bonded structure of DNA. 4. It is concluded that a process was occurring during gamma-irradiation of DNH that, although involving a decrease in molecular weight, did not diminish and even enhanced its priming ability. This is consistent with previous physicochemical evidence that gamma-irradiation causes dissociation of histone from DNH.

Adenine Nucleotides↗
PubMed1966

The inhibition of ribonucleic acid polymerase by acridines.

1. The aminoacridines, proflavine (3,6-diaminoacridine) and 9-aminoacridine, and a hydrogenated derivative, 9-amino-1,2,3,4-tetrahydroacridine, were shown to inhibit in vitro the DNA-primed RNA polymerase of Escherichia coli. The inhibition is strong with both proflavine and 9-aminoacridine, but weak with 9-amino-1,2,3,4-tetrahydroacridine. 2. The extent to which the three acridines bind to calf-thymus DNA in the enzyme medium was studied spectrophotometrically. The extent of binding decreases in the order: proflavine, 9-aminoacridine, 9-amino-1,2,3,4-tetrahydroacridine. Some evidence was also obtained for interaction between the nucleoside triphosphate substrates and proflavine or 9-aminoacridine; no such interaction was detectable with 9-amino-1,2,3,4-tetrahydroacridine. 3. Although the amount of acridine bound to DNA increases with increasing inhibition, a stage is reached where an increase in acridine concentration still causes an increase in inhibition, with practically no increase in the amount bound to DNA. 4. Plots of reciprocal rates against the reciprocal of DNA concentration were linear and had a common intercept when proflavine or 9-aminoacridine was present. Similar relations were obtained when the reciprocal concentration of nucleoside triphosphates was plotted. The observations are interpreted kinetically in terms of a competitive inhibition of the enzyme by proflavine or 9-aminoacridine and of a kinetic role for the DNA analogous to ;activation'. 5. This suggests that inhibitory acridine molecules can occupy the sites on the RNA polymerase that are specific for binding the nucleoside triphosphate substrate or the bases of the DNA, when these become accessible during the copying process.

Acridines↗
PubMedDate not supplied

Chemical basis of antigenic variation in foot-and-mouth disease virus.

One of the difficulties in controlling foot and mouth disease by vaccination is the occurrence of the virus as seven distinct serotypes because immunity conferred by vaccination against one serotype leaves the animals susceptible to infection by the other six. Moreover, the antigenic variation, even within a serotype, can be so great that immunity against the homologous strain of virus need not necessarily ensure protection against infection by other viruses within that serotype. Here we report the separation of three natural antigenic variants, distinguishable in cross-neutralization tests from an isolate of foot-and-mouth disease virus (FMDV). The serological differences could also be demonstrated by antisera elicited by synthetic peptides corresponding to residues 141-160 of the capsid polypeptide VP1, showing that this region contains a major immunogenic site of the virus. The results have practical implications for the choice of viruses for vaccine production.

Amino Acid Sequence↗