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F L Brown

Publications and source records attributed to F L Brown.

At least 19 recordsLinked to original sources
PubMed2000

Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction.

Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium.

Journal Article↗
PubMed2000

Regulation of protein mobility in cell membranes: a dynamic corral model.

We analyze a two-state stochastic corral model for regulation of protein diffusion in a cell membrane. This model could mimic control of protein transport in the membrane by the cytoskeleton. The dynamic corral acts as a gate which when open permits an otherwise trapped protein to escape to a neighboring corral in the cytoskeletal network. We solve for the escape rate over a wide range of parameters of the model, and compare these results with Monte Carlo simulations. Upon introducing measured values of the model parameters for Band 3 in erythrocyte membranes, we are able to estimate the value for one unknown parameter, the average rate at which the corral closes. The ratio of calculated closing rate to measured opening rate is roughly 100:1, consistent with a gating mechanism whereby protein mobility is regulated by dissociation and reassociation of segments of the cytoskeletal network.

Cell Membrane↗
PubMed2000

Lateral diffusion of membrane proteins in the presence of static and dynamic corrals: suggestions for appropriate observables.

We consider the possibility of inferring the nature of cytoskeletal interaction with transmembrane proteins via optical experiments such as single-particle tracking (SPT) and near-field scanning optical microscopy (NSOM). In particular, we demonstrate that it may be possible to differentiate between static and dynamic barriers to diffusion by examining the time-dependent variance and higher moments of protein population inside cytoskeletal "corrals." Simulations modeling Band 3 diffusion on the surface of erythrocytes provide a concrete demonstration that these statistical tools might prove useful in the study of biological systems.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1995

Induction of G2 arrest and gene expression by 2-aminopurine in human U937 promonocyte-macrophage cells.

The adenine analogue, 2-aminopurine (2-AP), induces G2 arrest in the human promonocyte-macrophage cell line, U937. The arrest is reversible and cells enter mitosis to resume normal logarithmic growth upon removal of the drug. These physiological changes are accompanied by markedly stimulated expression of eukaryotic gene constructs stably integrated in the chromosomes or introduced into the cells by transient transfection. Induction by 2-AP has two components: one involves increased transcription of the introduced genes as shown by run-on transcription experiments. The other involves markedly increased mRNA half-life that affects mRNA transcribed from transiently transfected DNA but apparently does not affect mRNA transcribed from the same chromosomally integrated sequences. Together, these two components could account for the 100- to 1000-fold inductions observed with various transfected gene constructs reported here and elsewhere. Maximum induction by 2-AP is promiscuous with respect to eukaryotic promoter origins or sequences, but appears to require a minimum of two such promoter elements. Thus, G2 cell cycle arrest induced by 2-AP is also associated with transcriptional and post-transcriptional alterations in gene expression. The data also suggest that transiently transfected DNAs may enter spatial or biochemical compartments of the nucleus that are different from those of normal genes in their native locations. These differences may affect the abundance and fate of the transcribed mRNA and, in some circumstances, introduce serious discordances into studies of gene regulation.

2-Aminopurine↗
PubMed1993

Inducible transcriptional activation of the human immunodeficiency virus long terminal repeat by protein kinase inhibitors.

The protein kinase inhibitor 2-aminopurine (2-AP) greatly stimulated expression in human promonocytes-macrophages of plasmid constructs carrying various reporter genes (chloramphenicol acetyltransferase, lacZ, firefly luciferase [luc], and Salmonella typhimurium histidinol dehydrogenase [his]) driven by the human immunodeficiency virus type 1 (HIV-1) long terminal repeat. Adenine, adenosine, and caffeine were also effective inducers, but other purine or pyrimidine derivatives were ineffective. Experiments with mutant derivatives of the HIV-1 long terminal repeat revealed no specific eukaryotic promoter elements necessary for 2-AP induction but indicated the need for some minimum combination of such elements. Induction of HIV-1-directed gene expression appeared not to require action of the transcription factor NF-kappa B. The mechanism of induction was investigated by using the luc and his genes linked to the HIV-1 long terminal repeat. 2-AP induced marked, steady rises in mRNA accumulation from both transfected and chromosomally integrated HIV-1 constructs but no increases from an endogenous gene encoding gamma-actin or glucose 6-phosphate dehydrogenase. Thus, induction is selective and not an artifact induced by transfecting DNA into cells. In run-on transcription experiments, the rates of transcription initiation of both transfected and integrated copies of the his gene increased about sixfold in cells treated with 2-AP. Thus, while increased initiation accounted for a portion of 2-AP induction, it could not cause the far greater increase in steady-state mRNA levels. 2-AP induction did not change mRNA decay rates and differed from the phorbol ester (phorbol myristate acetate)-induced activation of the protein kinase C-NF-kappa B pathway in its time course and in its requirement for new protein synthesis. Gel retardation assays showed that unlike phorbol myristate acetate induction, 2-AP induction is enhancer independent. Whereas many previous studies have implicated the activation of various protein kinases in gene induction, we here describe a mechanism of gene activation that appears to involve protein kinase inhibition as a component of the induction response.

2-Aminopurine↗
PubMed1991

Gene activation mediated by protein kinase C in human macrophage and teratocarcinoma cells expressing aminoglycoside phosphotransferase activity.

The bacterial neomycin phosphotransferase gene driven by the Moloney mouse leukemia virus long terminal repeat (LTR) or SV40 early region promoter was introduced into the human promonocyte-macrophage cell line, U937, and into the pluripotential human embryonic teratocarcinoma cell line, NT2/D1. Clonally derived cell lines capable of growing in 2-4 mg/ml of the aminoglycoside antibiotic, G418 (Geneticin), were established and transfected with pHIVCat, a plasmid expressing the bacterial chloramphenicol acetyl transferase (CAT) activity under the control of the human immunodeficiency virus (HIV-1) LTR. All of the G418 resistant (neo(r)) U937 cell lines and 10 of 14 neo(r) NT2/D1 cell lines exhibited reduced basal levels of CAT expression or impaired responses to activation of the HIV-1 LTR by phorbol 12-myristate 13-acetate (PMA) when compared to the parental lines. Other differences included inhibition of tat activation of the HIV-1 LTR and increased sensitivity of U937 cells to human tumor necrosis factor alpha. The expression of other eukaryotic promoters including the HTLV-1 LTR, SV40 ori sequences, and the human beta-actin gene promoter was similarly affected. However, differentiation of the neo(r) U937 cells into macrophages was neither delayed nor impaired. Because PMA is an activator of protein kinase C (PKC) and a potent inducer of HIV-1 directed gene expression, the amounts, sensitivity to G418, and cytosol to membrane translocation of this enzyme were determined in the wild type and neo(r) U937 cells. G418 at concentrations too low to affect cell growth (12-150 micrograms/ml) inhibited PMA-induced transactivation responses in wild type cells but did not inhibit PKC-dependent protein phosphorylation in vitro. PKC activities in the wild type and neo(r) cells were similar in absolute amounts and in the cytosol-membrane distribution of the enzyme. In contrast with wild type cells, however, all of the cytosolic Ca(2+)-phospholipid-dependent form of PKC disappeared from the neo(r) cells within 30 min after PMA induction. The results suggested that, depending upon the cell type, gene cotransfer using aminoglycoside resistance as a selectable marker may seriously perturb important cellular control mechanisms such as the PKC pathway leading to activation of gene expression.

Blotting, Northern↗
PubMed1991

Systems face challenges. Interview by Donald E.L. Johnson.

The regional hospital system has become a mainstay in the structuring of health care during the past decade. How will it fare in the next 10 years? In the following interview with Health Care Strategic Management's editor and publisher Donald E.L. Johnson, Fred L. Brown, president and chief executive officer of Christian Health System, the St. Louis, Mo.-based umbrella organization for nine hospitals, six nursing facilities, and one retirement community, predicts a bright future for the health care system. He also discusses the strategies that are unique to the success of such a system.

Christianity↗
PubMed1988

Regulation of expression driven by human immunodeficiency virus type 1 and human T-cell leukemia virus type I long terminal repeats in pluripotential human embryonic cells.

Human pluripotential embryonic teratocarcinoma cells differentially expressed gene activity controlled by the human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type I (HTLV-I) long terminal repeats (LTRs) when differentiation was induced by the morphogen all-trans retinoic acid. The alterations occurred after commitment and before the appearance of the multiple cell types characteristic of these pluripotential cells. After commitment, gene activity controlled by the HIV-1 LTR markedly increased, whereas that controlled by the HTLV-I LTR decreased. Steady-state mRNA levels and nuclear run-on transcription indicated that the increased HIV-1-directed activity during differentiation occurred posttranscriptionally, whereas the decreased HTLV-I activity was at the transcriptional level. Phorbol esters did not cause commitment but strongly enhanced expression by both viral LTRs at the transcriptional level. A specific inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, indicated that the enhanced activity involved the activation of protein kinase(s) C; altered cyclic nucleotide metabolism was apparently not involved. Differentiating cells gradually lost the ability to respond to phorbol ester stimulation. Experiments with a deletion mutant of the HIV-1 LTR suggested that this was due to imposition of negative regulation during differentiation that was not reversed by phorbol ester induction. Cycloheximide, with or without phorbol ester, slightly stimulated HIV-1-directed activity at the transcriptional level and massively increased the amounts of steady-state mRNA by posttranscriptional superinduction. It appeared, however, that new nuclear protein synthesis was required for maximal transcriptional stimulation by phorbol esters. Thus, changing cellular regulatory mechanisms influenced human retrovirus expression during human embryonic cell differentiation.

Cell Differentiation↗
PubMed1986

Comparison of diflunisal and acetaminophen with codeine in the treatment of initial or recurrent acute low back strain.

Effective pain relief and patient tolerance and acceptance are essential in outpatient management of mild to moderate pain of acute low back strain. This study evaluated the efficacy, tolerability, and acceptability of diflunisal and acetaminophen with codeine in patients with mild to moderate pain after an initial or recurrent acute low back strain. Both drugs demonstrated equipotent analgesic efficacy; however, diflunisal was superior to acetaminophen with codeine for patient tolerability and acceptability. The results demonstrated that the study drugs were effective in treating mild to moderate pain caused by acute low back strain in an ambulatory care setting.

Acetaminophen↗
PubMed1982

KpnI families of long, interspersed repetitive DNAs in human and other primate genomes.

KpnI restriction of DNAs from all anthropoid primates studied releases a conspicuous series of segments representing families of long, interspersed repetitive DNAs termed here the KpnI 1.2, 1.5, 1.8 and 1.9 kb families. Human KpnI 1.2 to 1.9 kb segments representative of these families were isolated and separately cloned in the KpnI site of a plasmid pBK5, specially constructed for this purpose. The KpnI clones did not cross-hybridize with cloned, primate alphoid sequences, suggesting that the KpnI families represent sequences separate and distinct from the alphoid DNAs. Secondary restriction analyses of cloned KpnI segments demonstrated microheterogeneity among individual members within the same KpnI family. Autoradiograms of capuchin monkey, AGM and human DNA cleaved with HaeIII, AluI or RsaI and hybridized to various cloned human KpnI sequences demonstrated a remarkable conservatism and relative simplicity in the organization of the KpnI families in the genomes of these widely divergent primates. The KpnI 1.2 kb and 1.5 kb families occur in high frequency (15%) among all plaques in two recombinant human genome libraries. Evidence is presented suggesting that the bulk of the KpnI families occur in the genome as clusters or congeries of higher molecular weight segments (greater than 2 kb) containing sequences homologous to the low molecular weight segments (1.2 to 1.9 kb).

Animals↗
PubMed1982

KpnI families of long, interspersed repetitive DNAs associated with the human beta-globin gene cluster.

KpnI families of long, interspersed repetitive DNAs are ubiquitous repetitive elements that occur in tens of thousands of copies in primate genomes. KpnI 1.2, 1.5 and two different KpnI 1.8-kb families were found within and flanking a 6.4-kb repeat beginning at 3 kb, 3' from the human beta-globin gene. Thus, six different types of KpnI families have now been identified, and four of these are found next to each other in a specific 6.4-kb repeat. Clones of the distinct KpnI families were hybridized to clones of the 6.4-kb repeat and adjacent sequences encompassed within some 17.6 kb of DNA lying 3' to the beta-globin gene cluster. The four KpnI families appear to make up the entire length of the 6.4-kb repeat. The linear order of the various cloned KpnI sequences in the repeat is 5'-pBK(1.8)26-pBK(1.5)54-pBK(1.2)11-pBK(1.8)11-3'. KpnI 1.2-kb sequences were also detected downstream from the 6.4-kb repeat. As in the case of the KpnI 1.2 and 1.5-kb families, the two KpnI 1.8-kb sequence families described here each hybridized with about 15% of all plaques in two independently generated human genome libraries.

DNA Restriction Enzymes↗
PubMed1982

Nucleosome phasing and micrococcal nuclease cleavage of African green monkey component alpha DNA.

The micrococcal nuclease cleavage of intact nuclear chromatin from African green monkey cells and of the completely deproteinized sequences was studied by using high-resolution analytical and DNA sequencing gels and secondary restriction enzyme analysis. When deproteinized component alpha DNA was used as substrate, not all phosphodiester bonds in the 172-base-pair repeat units were cleaved with equal frequency by the nuclease. A distinct preference for the cleavage of A-T rather than G-C bonds was observed; however, A + T-richness in itself did not confer susceptibility to cleavage by micrococcal nuclease. The results suggested that, in deproteinized DNA, nuclease cleavage at particular dinucleotides may be influenced more by the effect of adjacent sequences than by the composition of the dinucleotide. In contrast to complex cleavage patterns of the deproteinized component alpha DNA which arose because of multiple cleavage sites in the repeat unit, micrococcal nuclease cleaved component alpha nuclear chromatin at one site per nucleosome repeat, near position 126 in the nucleotide sequence. This simple chromatin cleavage pattern is consistent with the discrete nucleosomal structure of component alpha in chromatin and a direct phase relationship between the component alpha DNA sequence repeats and the nucleosome protein structural repeats.

Animals↗
PubMed1981

Toward a molecular paleontology of primate genomes. I. The HindIII and EcoRI dimer families of alphoid DNAs.

Families of related, but nonidentical repetitive DNA sequences, termed the alphoid DNAs, have been identified and characterized in representative species from seven major primate Families. The sequences appear as old as the primate Order itself: they are found in a prosimian (lemur), in a New World monkey, and in all Old World primates examined, including man. The alphoid DNAs are uniquely primate sequences and they may represent the most abundant repetitive DNAs in the primate genome. - A classification scheme for two major families of alphoid DNAs is proposed that is based upon restriction enzyme analysis and Southern blotting with radioactive probes prepared from component alpha DNA (Maio, 1971) and from the human EcoRI dimer sequences (Manuelidis, 1976). The family of alphoid DNAs that hybridizes readily with component alpha is termed the HindIII family of alphoid DNAs. This family shows an almost universal distribution among present-day primates. The family of DNA sequences that hybridizes readily with the human EcoRI dimer probe is termed the EcoRI dimer family of alphoid DNAs. This family may be restricted to the great apes and man. The two probes permitted the discrimination of different, but related alphoid families in present-day primates. Multiple alphoid sequence families are found within the genomes of individual primates and the major primate taxa can be characterized by the representations of the various alphoid DNAs within their genomes. - An Appendix is presented (Brown et al., 1981) indicating that competition hybridization effects may influence the autoradiographic banding patterns, and hence, the interpretations of Southern filter-transfer hybridizations when dealing with related repetitive sequences such as the alphoid DNAs that are present in abundance in eukaryotic genomes.

Animals↗