Flanking AT-rich sequences may lower the activation energy of cruciform extrusion in supercoiled DNA

In the absence of flanking AT-rich segments, cruciform transition energies of DNA palindromic sequences of random base composition are high and mainly dependent upon the base-stacking and -pairing parameters of the palindromic segment. When AT-rich sequences adjoin palindromes, the transition energy of cruciform extrusion is significantly lowered. An inverse relationship exists between the length of the AT-rich stretch and the cruciform transition energy. Long stretches lower the transition energies more than short stretches. At physiological salt and temperature conditions, equilibrium between cruciform extrusion and absorption for the inverted repeat sequences IRS-B and IRS-C of pBR322 derived plasmids is reached in less than five minutes.

Strategies of immune reconstitution: effects of lymphokines on murine T cell development in vitro and in vivo

Need for more effective treatment to reconstitute T cell immunity in secondary immunodeficiencies like AIDS prompted an exploration into the roles played by leukocyte products on the ontogeny of murine T lymphocytes in vitro and in vivo. It was observed that mixed lymphokines potently stimulate the proliferation of prothymocytes, immature cortical thymocytes, and mature medullary thymocytes. The effect of the natural, mixed lymphokines could be reproduced in the main by the combination of recombinant interleukin I and II. Mixed lymphokines administered in vivo augmented splenic lymphoproliferative responses in athymic nude mice without T cell marker (Thy 1.2) induction and, in neonatal mice, induced both Thy 1.2 and proliferative responses. Recombinant IL-2 at equivalent dose was less active in nude mice and not active in neonatal mice. The evidence indicates that lymphokines, particularly IL-1 and IL-2 in combination, regulate T cell ontogeny and can act in an endocrine fashion to promote T cell development in T cell-free mice having a functional thymus. Mixed lymphokines may be useful for immune reconstitution in AIDS, however, only if given prior to thymic destruction.

Nucleotide sequence of a chromosomal mercury resistance determinant from a Bacillus sp. with broad-spectrum mercury resistance

A 13.5-kilobase HindIII fragment, bearing an intact mercury resistance (mer) operon, was isolated from chromosomal DNA of broad-spectrum mercury-resistant Bacillus sp. strain RC607 by using as a probe a clone containing the mercury reductase (merA) gene. The new clone, pYW33, expressed broad-spectrum mercury resistance both in Escherichia coli and in Bacillus subtilis, but only in B. subtilis was the mercuric reductase activity inducible. Sequencing of a 1.8-kilobase mercury hypersensitivity-producing fragment revealed four open reading frames (ORFs). ORF1 may code for a regulatory protein (MerR). ORF2 and ORF4 were associated with cellular transport function and the hypersensitivity phenotype. DNA fragments encompassing the merA and the merB genes were sequenced. The predicted Bacillus sp. strain RC607 MerA (mercuric reductase) and MerB (organomercurial lyase) were similar to those predicted from Staphylococcus aureus plasmid pI258 (67 and 73% amino acid identities, respectively); however, only 40% of the amino acid residues of RC607 MerA were identical to those of the mercuric reductase from gram-negative bacteria. A 69-kilodalton polypeptide was isolated and identified as the merA gene product by examination of its amino-terminal sequence.

Homologous metalloregulatory proteins from both gram-positive and gram-negative bacteria control transcription of mercury resistance operons

We report the overexpression, purification, and properties of the regulatory protein, MerR, for a chromosomally encoded mercury resistance determinant from Bacillus strain RC607. This protein is similar in sequence to the metalloregulatory proteins encoded by gram-negative resistance determinants found on transposons Tn21 and Tn501 and to a predicted gene product of a Staphylococcus aureus resistance determinant. In vitro DNA-binding and transcription experiments were used to demonstrate those purified Bacillus MerR protein controls transcription from a promoter-operator site similar in sequence to that found in the transposon resistance determinants. The Bacillus MerR protein bound in vitro to its promoter-operator region in both the presence and absence of mercuric ion and functioned as a negative and positive regulator of transcription. The MerR protein bound less tightly to its operator region (ca. 50- to 100-fold) in the presence of mercuric ion; this reduced affinity was largely accounted for by an increased rate of dissociation of the MerR protein from the DNA. Despite this reduced DNA-binding affinity, genetic and biochemical evidence support a model in which the MerR protein-mercuric ion complex is a positive regulator of operon transcription. Although the Bacillus MerR protein bound only weakly to the heterologous Tn501 operator region, the Tn501 and Tn21 MerR proteins bound with high affinity to the Bacillus promoter-operator region and exhibited negative, but not positive, transcriptional control.

Oxidative detection of coulometrically reduced organonitro pesticides in reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic system is presented for determination of organonitro pesticides, metabolites and industrial chemicals having a variety of chemical structures. The compounds are chromatographed on a C8 column with an acetonitrile-aqueous ammonium monochloroacetate gradient. The chromatographic responses of the compounds are monitored indirectly by oxidative detection of the coulometrically reduced organonitro functionality by means of a porousgraphite detector. Three nitrophenols (2,4-dinitrophenol, 4,6-dinitro-o-cresol and dinoseb), a dinitrophenyl aliphatic ester (binapacryl) and a nitroaniline (dicloran) were detected at low nanogram levels (3-10 ng for 50% recorder full-scale deflection). This technique overcomes the problems of high background currents and oxygen interference, observed in the direct reductive detection of organonitro compounds.

Characterization of the atrial natriuretic peptide clearance receptor using a vaccinia virus expression vector

A recombinant vaccinia virus has been used to direct the expression of the atrial natriuretic peptide clearance receptor (ANP C-receptor) in mammalian cell lines normally deficient in this protein. The recombinant receptor binds 125I-ANP-(102-126) in a specific and saturable manner and carboxyl-terminal truncated and internal-deleted ANP analogs bind to this site with high affinity. Following the covalent attachment of 125I-ANP-(102-126) to the recombinant ANP C-receptor, the protein exhibits an electrophoretic mobility identical to that of the native ANP C-receptor of cultured vascular cells. Expression of the ANP C-receptor in heterologous cells does not affect ANP-stimulated cyclic GMP accumulation, confirming previous reports that this novel ANP receptor subpopulation is not coupled to cyclic GMP metabolism. Furthermore, specific antisera, generated by inoculating rabbits with living recombinant virus, block 125I-ANP binding to the ANP C-receptor but do not inhibit ANP stimulation of cyclic GMP, supporting the existence of two receptor subpopulations that are functionally and immunologically distinct.

Association of microinjected myosin and its subfragments with myofibrils in living muscle cells

Purified skeletal muscle myosin was labeled with iodoacetamidofluorescein and microinjected into cultured chick myotubes. The fluorescent myosin analogue became incorporated within 10-15 min after injection, into either periodic (mean periodicity = 2.23 +/- 0.02 micron) bands or apparently continuous fibrillar structures. Comparison of rhodamine-labeled alpha-actinin with coinjected fluorescein-labeled myosin suggested that myosin fluorescence was localized at the A-bands of myofibrils. In addition, close examination of the fluorescent myosin bands indicated that they were composed of two fluorescent bars separated by a nonfluorescent line that corresponded to the H-zone. Once incorporated, the myosin underwent a relatively slow exchange along myofibrils as indicated by fluorescence recovery after photobleaching. Glycerinated myofibrils were able to bind fluorescent myosin in a similar pattern in the presence or absence of MgATP, indicating that actin-myosin interactions had little effect on this process. Fluorescent heavy meromyosin did not incorporate into myofibrillar structures after injection. Light meromyosin, however, associated with A-bands as did whole myosin. These results suggest that microinjected myosin, even with its relatively low solubility under the cytoplasmic ionic condition, is capable of association with physiological structures in living muscle cells. Additionally, the light meromyosin portion of the molecule appears to be mainly responsible for the incorporation.

[Preclinical evaluation of a new anthracycline derivative, SM-5887 by subrenal capsule assay]

SM-5887, a new totally synthetic anthracycline derivative was evaluated the antitumor activity by subrenal capsule assay (SRCA) and the activity was compared to that of doxorubicin. The method of SRCA was the same originally developed by Bogden et al and 200 mg/kg of bredinin was administered subcutaneously 3 times every 2 days in order to induce immunosuppression of mice. Mice were given a single intravenous dose of either 30 mg/kg of SM-5887 or 15 mg/kg of doxorubicin. Fourty-four cases out of 64 were evaluable in this assay. The mean tumor growth inhibition rate (TGIR) in either SM-5887 or doxorubicin group was similar and the TGIRs of these two groups correlated well (y = 10.4 + 0.67x, p less than 0.01). Using more than 50% decrease of TGIR to define "sensitive", the chemosensitivity rates of SM-5887 and doxorubicin were 23% (10/44) and 25% (11/44) respectively. SM-5887 was effective to sarcomas and ovarian cancer especially. These results suggest that SM-5887 might have a similar antitumor activity compared to doxorubicin in clinical use.

The detection of early femoro-distal vein graft stenosis by treadmill exercise testing

A prospective study of 125 femoro-distal vein bypass grafts (103 patients) was undertaken to assess the role of treadmill exercise testing in the detection and correction of early vein graft stenosis. Patients were followed at 1,3,6,12 months and then annually with routine clinical assessment, palpation of pulses and resting Doppler ankle/brachial index. In addition, the Doppler index was repeated after 5 minutes exercise on a treadmill set at 5 degrees and 3 km/hr. Follow-up has been carried out for a mean of 24 months (range 3-48 months) and during that time 30 vein grafts (28 patients) were submitted to angiography. This revealed vein graft stenosis in 15, native vessel disease in 11 and no morphologic abnormality in 4. One additional graft was suspected to have a stenosis but occluded before angiography could be carried out. At the time of detection by the treadmill test, 8 of the 15 (53%) confirmed vein graft stenoses, and 4 of 11 (36%) native vessel stenoses would not have been detected by clinical assessment or resting Doppler pressure measurements. The 15 vein graft stenoses which were corrected all remain patent, suggesting that treadmill testing is of value in the detection and prevention of early femoro-distal vein graft occlusion.

Chromosome and growth factor abnormalities in melanoma

Cultures from metastatic melanomas of 15 patients had detailed melanoma growth stimulatory activity (MGSA) and cytogenetic analysis. The presence of melanoma cells was confirmed by microscopic identification of melanin, tyrosinase activity, and electron microscopy characterization of melanosomes. The MGSA is found in cytoplasmic granules after immunocytochemical stain. Three of the cultures did not produce MGSA and showed no distinctive cytogenetic differences. Breakpoints in derivative chromosomes were concentrated in region 1p1, and among all cultures chromosome 1 was the most frequently rearranged. It also has a low copy number of normal homologs. Chromosomes 18, X, and Y were never derivative, and chromosomes 2 and 4 were rarely so. Thus the cytogenetic data indicate that 4q13-21, the hybridization site for MGSA cDNA, is spared from gross change, although it could be under the influence of another site on chromosome 1 that is lost or rearranged. The ratio of abnormal to normal autosomes (mean per cell) in no culture exceeded 0.5, and for no autosome exceeded 0.8, suggesting a limit to the rearrangement tolerated for cell survival. If the Y is retained, the X:Y ratio varies around a normal figure of 1. The ratio of autosomes to sex chromosomes varies around a normal figure of 22. These data suggest stability of the X chromosome in cells undergoing multiple rearrangements of the autosomes.

Paramedian reticular nucleus--sympathetic inhibition in spontaneously hypertensive rats

The cardiovascular reactivity of various areas in the medulla related to sympathetic or parasympathetic activation, or to sympathetic inhibition, was compared in spontaneously hypertensive rats (SHR) and in normotensive rats Wistar-Kyoto (WKY) or Sprague-Dawley (SD). In SHR, which has an elevated resting systemic arterial blood pressure (SAP), the sympathetic pressor responses elicited from electrical stimulation of the dorsomedial medulla (DMM), parvocellular lateral nucleus (PVC) or ventrolateral medulla (VLM) were more profound than those in WKY and SD. The depressor and bradycardia responses elicited from electrical stimulation of the paramedian reticular nucleus (PRN) (which exerts both sympathetic and parasympathetic inhibitions) or from the area of the solitary nucleus/dorsomotor nucleus of vagus (NTS/DMV) (where stimulation leads to both parasympathetic activation and sympathetic inhibition) were also more intensive in SHR than in WKY and SD. The elicited pressor and depressor responses, however, were not significantly different between WKY and SD. Our results are consistent with previous findings (15) that in SHR an increased sympathetic activity of the pressor areas of medulla contributes to the pathogenesis of hypertension. Sympathetic inhibition (PRN and NTS/DMV areas) and parasympathetic activation (NTS/DMV area) from these areas, however, may not be critically involved.

GaAlAs laser diode frequency locked at the D(2) line of Cs atoms in an atomic beam

A GaAlAs laser diode has been locked to the D(2)transition of Cs atoms in an atomic beam. Measured frequency stabilities are 1 x 10(-10) (0.1 sec), 8.4 x 10(-12) (1 sec), 2.2 x 10(-12) (10 sec), and 7.8 x 10(-13) (100 sec). This system has been successfully applied to an optically pumped Cs-beam frequency standard.

Fluorescent modification of the cysteine 202 residue of Escherichia coli transcription termination factor rho

The lone cysteine residue (Cys-202) of transcription termination factor rho has been modified with the sulfhydryl-specific dyes 5-iodoacetamidofluorescein and 5-(2-[iodoacetyl)amino)ethyl)aminonaphthalene-1-sulfonic acid. Labeling with both dyes is specific for the Cys-202 residue and is at least 90% complete. Rho protein is an RNA-dependent ATPase and exists as a hexamer of identical subunits in its activated (RNA-liganded) form. We find that chemical modification of rho at Cys-202 does not significantly change the properties of the protein; subunit assembly, RNA binding, and poly(rC)-activated ATP hydrolysis are all relatively unperturbed by the covalent attachment of these fluorescent moieties. On the other hand, the spectral, quenching, and anisotropy properties of the fluorescent groups are all significantly modified by attachment to the protein. No energy transfer is seen between fluorescein-labeled subunits within rho hexamers, indicating that the Cys-202 residues on these subunits are located at least 40 A apart. These fluorescently labeled rho molecules should represent useful probes to study the conformations and inter- and intrasubunit geometries of this termination factor at various stages of its interaction with nascent RNA transcripts.