PubMed Health⌕ Search

Biomedical subjects

A D Frankel

Publications and source records attributed to A D Frankel.

68 records · Page 4Linked to original sources
PubMed1989

Inhibition of antigen-induced lymphocyte proliferation by Tat protein from HIV-1.

The purified human immunodeficiency virus type-l (HIV-l) Tat protein inhibited lymphocyte proliferation induced by tetanus toxoid or Candida antigens by 66 to 97% at nanomolar concentrations of Tat. In contrast, Tat did not cause a significant reduction of lymphocyte proliferation in response to mitogens such as phytohemagglutinin or pokeweed mitogen. Inhibition was blocked by oxidation of the cysteine-rich region of Tat or by incubation with an antibody to Tat before the assay. A synthetic Tat peptide (residues 1 to 58) also inhibited antigen-stimulated proliferation. Experiments with H9 and U937 cell lines showed that Tat can easily enter both lymphocytes and monocytes. The specific inhibition of antigen-induced lymphocyte proliferation by Tat mimics the effect seen with lymphocytes from HIV-infected individuals and suggests that Tat might directly contribute to the immunosuppression associated with HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Activity of synthetic peptides from the Tat protein of human immunodeficiency virus type 1.

To determine which of the 86 amino acids in the Tat protein of human immunodeficiency virus type 1 (HIV-1) are important for transactivation, peptides from Tat were synthesized and their activity was measured in cells containing a chloramphenicol acetyltransferase reporter gene under control of the HIV long terminal repeat promoter. Although the Tat sequence contains arginine- and cysteine-rich stretches that are difficult to synthesize, it was possible to prepare pure peptides in good yield by using fluoren-9-ylmethoxycarbonyl (Fmoc) chemistry. A peptide containing residues 1-58 had 5-10% the activity of full-length Tat. Deleting 4 amino acids from the N terminus of this peptide further reduced activity, while peptides with more extensive N-terminal deletions and peptides missing the basic region at the C terminus had no detectable activity. A peptide previously reported to transactivate, Tat-(37-62), was completely inactive in our assays. Inactive peptides were also tested as possible inhibitors of transactivation. Tat-(21-38), which contains the cysteine-rich region and can form heterodimers with intact Tat in vitro, showed inhibition at high peptide concentrations. However, this effect was not specific for Tat or for the HIV promoter, since the peptide also inhibited expression from the simian virus 40 early promoter.

Amino Acid Sequence↗
PubMed1988

Cellular uptake of the tat protein from human immunodeficiency virus.

While developing an assay to measure the activity of the tat protein from human immunodeficiency virus 1 (HIV-1), we discovered that the purified protein could be taken up by cells growing in tissue culture and subsequently trans-activate the viral promoter. Trans-activation is dramatically increased by a variety of lysosomotrophic agents. For example, trans-activation can be detected at tat concentrations as low as 1 nM in the presence of chloroquine. Experiments using radioactive protein show that tat becomes localized to the nucleus after uptake and suggest that chloroquine protects tat from proteolytic degradation. These results raise the possibility that, under some conditions, tat might act as a viral growth factor to stimulate viral replication in latently infected cells or alter expression of cellular genes.

Animals↗
PubMed1988

Combining thermostable mutations increases the stability of lambda repressor.

We have combined three mutations previously shown to stabilize lambda repressor against thermal denaturation. Two of these mutations are in helix 3, where Gly-46 and Gly-48 have been replaced by alanines [Hecht, M. H., et al. (1986) Proteins: Struct., Funct., Genet. 1, 43-46]. The other mutation, which replaces Tyr-88 with cysteine, allows the protein to form an intersubunit disulfide bond [Sauer, R. T., et al. (1986) Biochemistry 25, 5992-5998]. Calorimetric measurements show that the two alanine substitutions stabilize repressor by about 8 degrees C, that the disulfide bond stabilizes repressor by about 8 degrees C, and that the triple mutant is 16 degrees C more stable than wild-type repressor.

Amino Acid Sequence↗
PubMed1988

Tat protein from human immunodeficiency virus forms a metal-linked dimer.

Tat, the transactivating protein from HIV, forms a metal-linked dimer with metal ions bridging cysteine-rich regions from each monomer. This novel arrangement is distinct from the "zinc finger" domain observed in other eukaryotic regulatory proteins. Ultraviolet absorption spectra show that Tat binds two Zn2+ or two Cd2+ ions per monomer, and electrophoresis of the Tat-metal complexes demonstrates that the protein forms metal-linked dimers. Partial proteolysis and circular dichroism spectra suggest that metal binding has its primary effects in the cysteine-rich region and relatively little effect on the folding of other regions. These results suggest new directions for biological studies and new approaches to drug design.

Cadmium↗
PubMed1988

Dimerization of the tat protein from human immunodeficiency virus: a cysteine-rich peptide mimics the normal metal-linked dimer interface.

We have synthesized an 18-amino acid peptide that contains the cysteine-rich region of the tat protein from human immunodeficiency virus. Previous experiments in vitro with the intact tat protein have shown that these cysteines serve as metal ligands, causing tat to form metal-linked dimers. Ultraviolet absorption spectra show that the synthetic peptide (tat21-38) binds two Cd2+ or two Zn2+ ions per peptide monomer, and some changes in the circular dichroism spectra are seen as the metals bind. The peptide-metal complexes are completely resistant to proteolytic digestion, and mass spectrometry demonstrates that this peptide forms metal-linked dimers. The peptide can also combine with the intact tat protein to form metal-linked heterodimers. If these heterodimers are unable to trans-activate viral transcription, tat21-38 could be a lead compound for designing drugs to treat acquired immunodeficiency syndrome.

Amino Acid Sequence↗
PubMed1988

Hemisphericity and problem-solving ability.

149 freshmen undergraduates were administered the Higher Information Processing Scale and an anagram problem-solving task. Single-solution anagrams were chosen from lists of age-appropriate vocabulary words high in concrete imagery or low in imagery (abstract). Small but significant correlations were obtained between number of concrete anagrams solved and right- and integrated-hemispheric preference scores, respectively. Students categorized as "integrated preference" solved more high-imagery anagrams than any other group. Results lend support to the hypothesis that brain hemisphere specializations may exist but integration of the hemispheres may yield best performance.

Adult↗
PubMed1987

Metal-dependent folding of a single zinc finger from transcription factor IIIA.

A 30-amino acid peptide, which corresponds to the second "zinc finger" domain of transcription factor IIIA, has been synthesized and purified. This peptide folds in the presence of zinc: adding Zn2+ significantly changes the circular dichroism spectrum, and Zn2+ protects the peptide from tryptic digestion. The peptide also binds Co2+, and the absorption spectrum of the Co2+ complex suggests that a tetrahedral binding site is formed by two cysteines and two histidines. Experiments at higher temperatures (60-75 degrees C) suggest that these folded metal-peptide complexes are quite thermostable. The peptide shows some sequence-specific effects in DNase and methylation protection experiments. However, it does not give a clear "footprint," and some effects are observed in the absence of added zinc.

Amino Acid Sequence↗
PubMed1985

Measurement of DNA-protein equilibria using gel chromatography: application to the HinfI restriction endonuclease.

A method is described for measuring equilibrium constants of DNA-protein interactions using gel chromatography. This technique has been used to study the sequence-specific interaction of the HinfI restriction endonuclease with DNA. HinfI has a monomeric molecular weight of 31000 and exists as a dimer in its active form. The protein binds to supercoiled DNA molecules containing its recognition site with an apparent free energy of -13.9 kcal/mol of sites. This interaction is highly salt sensitive and causes a release of 3.4 ion pairs. The affinity of the nuclease for its recognition site is largely independent of both pH (6.5-8.5) and temperature (7-35 degrees C) and was not affected by variations in the degenerate middle position of the site. Linear DNA fragments containing the HinfI recognition site were bound as tightly as supercoiled molecules. Binding to nonspecific DNA sites or to methylated DNA sites was approximately 6 orders of magnitude weaker. In general, enzyme activity and binding affinity paralleled each other.

Chromatography, Gel↗
PubMed1983

Systematic analysis of possible hydrogen bonds between amino acid side chains and B-form DNA.

The ways in which amino acid side chains could make a pair of hydrogen bonds within the major groove of B DNA are systematically analyzed. Hydrogen bond donors within the major groove are characterized by determining the idealized position of the hydrogen bond acceptors that they might bond with. It appears that an amino acid side chain could, at most, contact a pair of base pairs. The ten possible pairs of base pairs are analyzed to determine how they could be recognized by the amino acid side chains.

Amino Acids↗
PubMed1980

Changes in enzyme activity during differentiation in Chlamydomonas reinhardtii.

The patterns of alanine dehydrogenase, glutamate dehydrogenase and malate dehydrogenase activity were studied during the normal vegetative cell cycle and during the processes of gametic differentiation and dedifferentiation in synchronized cultures of Chlamydomonas reinhardtii. During all three phases of growth and differentiation the synthesis of DNA was also measured. During gametic differentiation all three enzyme levels were suppressed compared to vegetative cells although DNA and cell number were comparable. During gametic dedifferentiation no DNA synthesis occurred during the first 24 h cycle and only a doubling during the second. It was not until the third cycle that a normal 4-fold increase in DNA was observed. Cell number followed a similar pattern. Although the levels of alanine dehydrogenase and malate dehydrogenase were uniformly low during the first cycle when glutamate dehydrogenase increased 4-fold, during the second cycle the patterns of these enzymes changed markedly. The enzymes did not attain levels characteristic of vegetative cells until the third cycle.

Alanine Dehydrogenase↗
PubMed1980

Nitrous acid damage to duplex deoxyribonucleic acid: distinction between deamination of cytosine residues and a novel mutational lesion.

The rate of nitrous acid deamination of labeled cytosine residues in native Escherichia coli deoxyribonucleic acid was monitored in vitro by release of acid-soluble counts after treatment with uracil deoxyribonucleic acid glycosylase. The reaction exhibited a lag and was not stimulate by several agents previously shown to enhance base substitution mutagenesis during nitrous acid treatment of duplex deoxyribonucleic acid. We conclude that a significant proportion of nitrous acid induced mutagenic lesions are novel lesions and not cytosine deaminations.

Cytosine↗