Nucleotide sequence and expression of the mercurial-resistance operon from Staphylococcus aureus plasmid pI258

The mercurial-resistance determinant from Staphylococcus aureus plasmid pI258 is located on a 6.4-kilobase-pair Bgl II fragment. The determinant was cloned into both Bacillus subtilis and Escherichia coli. Mercury resistance was found only in B. subtilis. The 6404-base-pair DNA sequence of the Bgl II fragment was determined. The mer DNA sequence includes seven open reading frames, two of which have been identified by homology with the merA (mercuric reductase) and merB (organomercurial lyase) genes from the mercurial-resistance determinants of Gram-negative bacteria. Whereas 40% of the amino acid residues overall were identical between the pI258 merA polypeptide product and mercuric reductases from Gram-negative bacteria, the percentage identity in the active-site positions and those thought to be involved in NADPH and FAD contacts was above 90%. The 216 amino acid organomercurial lyase sequence was 39% identical with that from a Serratia plasmid, with higher conservation in the middle of the sequences and lower homologies at the amino and carboxyl termini. The remaining five open reading frames in the pI258 mer sequence have no significant homologies with the genes from previously sequenced Gram-negative mer operons.

Cloning and DNA sequence of a plasmid-determined citrate utilization system in Escherichia coli

The citrate utilization determinant from a large 200-kilobase (kb) naturally occurring plasmid was previously cloned into the PstI site of plasmid vector pBR325 creating the Cit+ tetracycline resistance plasmid pWR61 (15 kb). Tn5 insertion mutagenesis analysis of plasmid pWR61 limited the segment responsible for citrate utilization to a 4.8-kb region bordered by EcoRI and PstI restriction nuclease sites. The 4.8-kb fragment was cloned into phage M13, and the DNA sequence was determined by the dideoxyribonucleotide method. Within this sequence was a 1,296-base-pair open reading frame with a preceding ribosomal binding site. The 431-amino-acid polypeptide that could be translated from this open reading frame would be highly hydrophobic. A second long open reading frame with the potential of encoding a 379-amino-acid polypeptide preceded the larger open reading frame. Portions of the 4.8-kb fragment were further subcloned with restriction endonucleases BglII and BamHI, reducing the minimum size needed for a citrate-positive phenotype to a 1.9-kb BamHI-BglII fragment (which includes the coding region for the 431-amino-acid polypeptide, but only the distal 2/3 of the reading frame for the 379-amino-acid polypeptide). Citrate utilization results from a citrate transport activity encoded by the plasmid. With the 4.8-kb fragment (as with larger fragments) the citrate transport activity was inducible by growth on citrate. On transfer from glucose, succinate, malate, or glycerol medium to citrate medium, the Cit+ Escherichia coli strains showed a delay of 36 to 48 h before growth.

Thyrotropin increases the iodine content of rat circulating thyroglobulin as measured by equilibrium density gradient centrifugation

In previous work we demonstrated that circulating thyroglobulin contains very little or no iodine. We have now characterized circulating thyroglobulin following administration of thyrotropin (TSH) to determine whether its iodine content remains low or increases after stimulation. The iodine content of circulating thyroglobulin was estimated from its density determined by equilibrium density gradient (isopycnic) centrifugation. TSH stimulated thyroglobulin from 182 +/- 28 ng/ml to 571 +/- 83 ng/ml at 8-14 h. Circulating thyroglobulin in the basal state had a density consistent with very little or no iodine. Its density increased following TSH to a maximum at 8-14 h which was nearly the same as the density of thyroglobulin extracted directly from the thyroid. To determine whether selective peripheral metabolism, based on the degree of iodination, could account for the density shift, purified rat thyroid thyroglobulin was injected into thyroidectomized rats. The density of thyroglobulin remained unchanged for 25 h during which time it was metabolized by more than 97%. Therefore, selective metabolism of thyroglobulin based on iodine content did not occur. We conclude that TSH causes a marked increase in the iodine content of circulating thyroglobulin. It is most likely that in the basal state circulating thyroglobulin comes from selective release of poorly iodinated molecules, while after TSH, it comes from release of previously synthesized, iodinated and stored molecules.

Somatomedin-C mediates growth hormone negative feedback by effects on both the hypothalamus and the pituitary

Somatomedin-C stimulates somatostatin release to a maximum of 390 percent of basal release during short-term (20-minute) incubation of rat hypothalamus. It has no effect on basal or stimulated growth hormone release from primary cultures of rat adenohypophyseal cells during a 4-hour incubation, but inhibits stimulated release by more that 90 percent after 24 hours. These findings suggest that somatomedin-C participates in the growth hormone negative feedback loop with an immediate effect on hypothalamic somatostatin and a delayed effect on the anterior pituitary.

Cellular characteristics of immunolabeled luteinizing hormone releasing hormone (LHRH) neurons

This study utilized the preembedding immunocytochemical technique in order to identify LHRH-containing neurons in rat brain and define their ultrastructural characteristics. LHRH-containing neurons in the vertical limb of the diagonal band of Broca, medial septum, triangular nucleus of the septum and other regions were studied by taking ultrathin serial sections. These neurons had scant cytoplasm surrounding a centrally-located, spheroid, euchromatic nucleus. Neurosecretory granules were evenly distributed throughout the cell, but many tended to lie directly under the plasmalemma. The cytoplasm was organized in such a way that the most extensive portion of the rough endoplasmic reticulum was polar opposite to areas having high concentrations of Golgi complex, lysosome-like bodies, smooth endoplasmic reticulum and ribosomes. The perikarya had no axosomatic synapses but functional interaction via unspecialized appositions to the plasmalemma cannot be discounted. Many of the perikarya bore at least one cilium. Processes from immunonegative cells were occasionally observed to penetrate the cytoplasm of the LHRH perikaryon or its processes. At their points of origin, dendrites were found to be broadened processes containing many elements common to the cytoplasm: ribosomes, smooth endoplasmic reticulum, cristal and lamellar mitochondria, neurotubules, and an occasional alveolate caveola. Infrequently, some of the LHRH axons were partially myelinated. This method of studying serial-sectioned immunocytochemically-identified cells is suggested as a means of describing the cellular and subcellular characteristics of other specific peptide-containing cells.

Primary in vitro cytotoxic response of NZB spleen cells to Qa-1b-associated antigenic determinants

We have shown that cytotoxic lymphocytes generated in primary cultures of NZB spleen cells with H-2-identical BALB/c or B10.D2 stimulator cells exhibit specificity for Qa-1b-associated antigenic determinants. This unidirectional cytotoxicity constitutes the initial demonstration of a primary in vitro response to antigens of the Qa-Tla system. Such responses do not require H-2 homology between effector and target cells in the assay system. In fact, when H-2Dd homologous target cells were employed there was little, if any, evidence for development of primary H-2-restricted responses to minor locus histocompatibility antigens or viral antigens. In view of the recently defined role of Qa-1+, Ly-1,2,3+ cells as regulators of antibody responses, and of the deficiency of such cells in NZB mice, the observation of hyperreactivity for determinants of this system may be relevant to the development of autoimmunity in these animals.

Regulatory mechanisms in cell-mediated immune responses. V. H-2 homology requirements for the production of a minor locus-induced suppressor factor

A mixed leukocyte reaction suppressor factor is produced by spleen cells sensitized in vivo and restimulated in vitro across non-H-2 antigenic barriers. Cells capable of producing this factor appear in the spleens of minor locus-immunized animals later than in animals sensitized to major histocompatibility complex-encoded antigens. However, both H-2 and non H-2-induced factors suppress proliferative responses to any alloantigen. Splenocytes from animals immunized with H-2-identical, minor locus-disparate cells produce suppressor factor in vitro only when restimulated with cells sharing both H-2 and non-H-2 antigens with the in vivo stimulators.

Sidedness of (sodium, potassium)-adenosine triphosphate of inside-out red cell membrane vesicles. Interactions with potassium

Inside-out membrane vesicles of human red cells, prepared according to the method of Steck et al. (1970) Science 168, 255-257) have sufficiently low cation permeability to allow the examination of the side-specific interactions of ligands with the asymmetric sodium pump complex. In accordance with the known properties of the pump in intact cells the following results were observed: (a) ATP-dependent sodium influx and (b) maximal (sodium, potassium)-ATPase with K+ present inside the vesicles with larger than or equal to 20 micronM ATP. With much lower [ATP], K+ inhibited sodium-activated ATPase. K+ was inhibitory at either surface. Inhibition was different on the two sides since cytoplasmic (extravesicular) Na+ counteracted inhibition by cytoplasmic (extravesicular) K+ but not inhibition by K+ at the plasma or external membrane surface, i.e. intravesicular K+. A decrease in the steady state level of the phosphenzyme intermediate of sodium-activated ATPase was caused also by K+ at either surface. The effect of cytoplasmic K+ is compatible with its competitive inhibition of activation of phosphorylation of the enzyme by cytoplasmic Na+. At 37 degrees, the inhibitory effect of external K+ is due to interaction with the phosphoenzyme to form a stable complex of K+ with the dephosphenzyme resulting in a decreased overall reaction rate but increased turnover of the phosphoenzyme (E-P + K leads to EK + Pi). At 0 degree, external K+ inhibits by interacting with the unphosphorylated enzyme to form an occluded enzyme-K complex. This results in a decreased overall rate but relatively small change in apparent turnover of the phosphoenzyme. At 0 degree, but not at 37 degrees, external Na+ counteracted the inhibitory effects of external K+.

Fractionation of lymphocyte subpopulations which regulate mixed lymphocyte reactions

Four days after injection of allogeneic lymphocytes BALB/c splenic T cells suppress proliferation of syngeneic cells in mixed lymphocyte reactions (MLR). Conversely, lymph node cells from the same mice amplify MLR responses. To further characterize these functional subpopulations, alloantigen-primed lymphocyte suspensions from both organs were fractionated by velocity sedimentation at unit-gravity. After fractionation MLR suppressor cells from spleens localized exclusively in rapidlly sedimenting fractions of large cells. MLR suppressor activity of cells from these fractions, as well as that of unfractionated spleen cell suspensions, was abolished by treatment with anti-Thy-1.2 serum and complement. Spleen cell fractions of similar sedimentation velocity also secreted a soluble MLR suppressor into culture supernatants. Although inhibitory of MLR, spleen cells of rapid sedimentation velocity did not suppress responses to T cell mitogens. In marked contrast with the effects of spleen cells, large 4-day-alloantigen-primed lymph node cells had no suppressive activity in MLR. MLR amplifier cells of uncertain derivation were found in fractions of medium sedimentation velocity from both spleens and lymph nodes. Fractionation of alloantigen-primed lymph node cell suspensions did reveal, however, a subpopulation of small cells with MLR suppressor acitivty which was unaffected by treatment with anti-Thy-1 serum and complement. The data thus indicate that large alloantigen-activated lymphocytes are not intrinsically suppressive nor are cells which suppress MLR necessarily large. We consequently conclude that regulation of MLR responses by alloantigen-primed lymphocytes involves a complex interaction between distinct functional subpopulations of cells which are separable both by physical and biologic properties.

Modifications of mammalian cell surfaces induced by sugars: scanning electron microscopy

Substitution of galactose, xylose, or mannose for glucose in the growth medium of L cells or the addition of equal concentrations of the alternate sugars to glucose-containing medium results in marked morphologic changes. The changes are revealed by conventional staining for light microscopy and by scanning electron microscopy. L cells grow indefinitely on combinations of equal concentrations of glucose and galactose, xylose, or mannose. There appear to be no significant differences in growth rate on glucose compared to the combinations of sugars cited. Cells subcultured from glucose to the combinations while undergoing rapid multiplication show marked morphologic changes by light and scanning electron microscopy within 36 hr. Of particular note are the loss of microvilli; flattening of the cells; assumption of polygonal shape; prominence of nuclei and nucleoli; and changes in the structure and distribution of filopodia. Virtually all cells in the population exhibit the changes noted.

Growth of pseudotypes of vesicular stomatitis virus with N-tropic murine leukemia virus coats in cells resistant to N-tropic viruses

Formation of pseudotypes between murine RNA tumor viruses and vesicular stomatitis virus (VSV) has been confirmed. Pseudotypes of VSV genomes coated by the surface envelope from an N-tropic tumor virus grew equally well in cells homozygous for either the Fv-1(n) or Fv-1(b) alleles. Therefore, the product of the Fv-1 locus, which restricts growth of murine RNA tumor viruses, must act on an intracellular aspect of tumor virus replication, a step after attachment and penetration.