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Biomedical subjects

J Portugal

Publications and source records attributed to J Portugal.

50 records · Page 3Linked to original sources
PubMed1987

Comparison of binding sites in DNA for berenil, netropsin and distamycin. A footprinting study.

Techniques of DNase I and micrococcal nuclease footprinting have been used to compare the binding sites for berenil, netropsin and distamycin on two different DNA fragments. Each ligand binds to the A + T-rich zones which contain clusters of at least four A.T base pairs. Neither guanosine nor cytidine nucleotides appear to be allowed within the A + T-rich runs which constitute the preferred binding sites, although they are sometimes protected from DNase I cleavage in neighbouring regions. Berenil and netropsin share with distamycin the property of causing enhanced rates of cleavage at certain sequences flanking their binding sites. There are significant differences in the concentrations of each ligand required to produce defined patterns of protection, seemingly dependent upon the nature (and possibly the gross base composition) of the piece of DNA being used in the experiment.

Amidines↗
PubMed1987

Interaction of nucleosome core particles with distamycin and echinomycin: analysis of the effect of DNA sequences.

Two fragments of Xenopus borealis DNA 135 and 189 base-pairs long were separately incorporated into nucleosome core particles by reconstitution with chicken erythrocyte histones, and incubated with echinomycin (a bis-intercalating antitumor antibiotic) or distamycin (a minor groove-binding, non-intercalating antibiotic). Controlled digestion of these defined sequence core particles using DNAase I revealed new cleavage products, indicative of a change in orientation of the DNA molecule on the surface of the nucleosome. This new rotational setting of DNA within the core particle induced by antibiotic binding appears to be practically independent of DNA sequence, although some differences were noted between the patterns of fragments observed in the various experiments, most likely reflecting the exact number and disposition of the antibiotic binding sites.

Animals↗
PubMed1987

Analysis of the effects of antibiotics on the structure of nucleosome core particles determined by DNAase I cleavage.

Patterns of sensitivity to DNAase I cleavage have been analysed in order to investigate the effects of anti-tumour antibiotics and related drugs on nucleosome core particles containing different DNA restriction fragments. In this article, we review the experimental results which show that after controlled digestion of defined-sequence core particles, new cleavage products appear in the enzyme digestion patterns which lie approximately mid-way between the strong bands characteristic of native nucleosome core particles. The effects of the antibiotics, which include bis-intercalators as well as minor groove-binding ligands (but not monofunctional intercalators), are explained in terms of an induced change in rotational setting (phasing) of the core DNA. The new rotational positioning of DNA induced by antibiotic binding appears to be almost independent of DNA sequence, although some differences can be observed with the various pieces of DNA, most likely reflecting the exact number and disposition of antibiotic binding sites.

Anti-Bacterial Agents↗
PubMed1987

The use of mechanical stimulation to obtain the sacral reflex latency: a new technique.

We determined sacral reflex latencies and morphologies in 18 neurologically normal patients and 83 with neurological disease by stimulating the glans penis or clitoris using electrical and a new technique of mechanical stimulation, and recording from the external urethral sphincter. The results with both stimulation techniques were compared among various diagnostic groups. In normal patients the mean sacral reflex latencies were 35.3 +/- 2.5 (standard deviation) msec. with electrical stimulation, and 39.1 +/- 4.0 msec. with mechanical stimulation. The mean reflex latencies in patients with lower motor neuron lesions studied by both methods were statistically longer than in normal subjects, and the mean reflex latencies in patients with upper motor neuron impairment studied by both methods were not statistically different from those in normal subjects. The morphological findings of the reflex tracings suggest that both types of evoked responses follow the same general anatomical pathway and both resemble a special human flexor reflex. The mechanical technique has advantages over the electrical technique because it is less painful and in certain instances it is easier to obtain.

Adult↗
PubMed1986

Antibiotics which can alter the rotational orientation of nucleosome core DNA.

Four well-characterised DNA-binding ligands have been tested for effects on reconstituted nucleosome core particles containing the 160 bp tyrT DNA fragment. Two, netropsin and berenil, were found to change the rotational orientation of the DNA on the surface of the protein as judged by marked alterations in the pattern of fragments produced by exposure to DNAase I. Qualitatively their effects were very similar to those previously reported for the related antibiotic distamycin, suggesting that the phenomenon of induced rotation may be a characteristic property of ligands which bind in the narrow groove of the DNA helix. Two intercalators did not produce the effect but, at high concentrations, caused gross disruption of the nucleoprotein structure with apparent release of DNA from the histone octamer. At moderate concentrations little or no effect was detectable with nogalamycin, suggestive of failure to bind as a result of constraints on local opening of the DNA helix. With moderate concentrations of actinomycin, protection of GpC sequences was clearly visible together with some evidence of increase in helix pitch, but no sign of altered phasing of DNA within the nucleosome core particles.

Anti-Bacterial Agents↗
PubMed1986

Influence of amino acid and peptide counterions on the conformation of DNA.

We describe fibre diffraction studies on the interaction of DNA with different amino acids and peptides. The B form of DNA, with ten base-pairs per turn, is always found at high levels of humidity. We suggest that this pitch is observed because the DNA molecules are maintained in a straight position. In solution, the DNA molecules are bent and may have a larger pitch. The A form of DNA is never found upon dehydration. Instead, the B form may be either stabilized by the counterions or altered so that the number of base-pairs per helical turn decreases upon dehydration. Alteration is favoured either by small counterions that have a single charge or by large basic polypeptides and proteins. Stabilization is favoured by small counterions that have several charged groups. A third type of behaviour is found with some amino acids that contain hydrophobic groups, which destabilize the secondary structure of DNA, probably due to a modification of its intramolecular interactions. We have not detected any specific effect of amino acid side-chains, although the amino acid sequence has a clear influence on the interaction. We think that these observations are of interest in the pursuit of more detailed crystallographic studies on protein-DNA interactions.

Amino Acids↗
PubMed1985

Counterions which favour the C form of DNA.

Recently the relationship between the B and C forms of DNA has been questioned. We have found some amino acids and related amines which form complexes with DNA and favour the C form. We have studied such complexes by X-ray diffraction. With some of these counterions the transition between the B and C forms occurs smoothly, whereas in other cases there is a discontinuous transition. We conclude that the C form is a well-defined variant of the B form favoured by some counterions under low humidity conditions.

Amino Acids↗