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1.
2.
Overexpression of the dnaA gene in Escherichia coli B/r: chromosome and minichromosome replication in the presence of rifampin. 总被引:7,自引:4,他引:3 下载免费PDF全文
O Pierucci C E Helmstetter M Rickert M Weinberger A C Leonard 《Journal of bacteriology》1987,169(5):1871-1877
The replication of chromosomes and minichromosomes in Escherichia coli B/r was examined under conditions in which the dnaA gene product was overproduced. Increased levels of the DnaA protein were achieved by thermoinduction of the dnaA gene, under the control of the lambda pL promoter, or by cellular maintenance of multicopy plasmids carrying the dnaA gene under the control of its own promoters. Previous work has shown that overproduction of DnaA protein stimulates replication of the chromosomal origin, oriC, but that the newly initiated forks do not progress along the length of the chromosome (T. Atlung, K. V. Rasmussen, E. Clausen, and F. G. Hansen, p. 282-297, in M. Schaechter, F. C. Neidhardt, J. L. Ingraham, and N. O. Kjeldgaard, ed., The Molecular Biology of Bacterial Growth, 1985). In the present study, it was found that overproduction of DnaA protein caused both a two- to threefold increase in the amount of residual chromosome replication and an extended synthesis of minichromosome DNA in the presence of rifampin. The amount of residual chromosome replication was consistent with the appearance of functional replication forks on the majority of the chromosomes. Since the rate of DNA accumulation and the cellular DNA/mass ratios were not increased significantly by overexpression of the dnaA gene, we concluded that the addition of rifampin either enabled stalled replication forks to proceed beyond oriC or enabled new forks to initiate on both chromosomes and minichromosomes, or both. 相似文献
3.
4.
We examined the effects of two enkephalin metabolites, des-tyr-[leu]enkephalin and tyr-gly-gly, on one-way active avoidance conditioning in mice. These metabolites are products of the two major enkephalin hydrolyzing enzymes in plasma, aminopeptidase and angiotensin converting enzyme. Like [leu]enkephalin from which it may be formed, tyr-gly-gly impaired avoidance acquisition, and its dose-response function for this effect was U-shaped. Also like [leu]enkephalin, tyr-gly-gly did not alter locomotor activity. On the other hand, des-tyr-[leu]enkephalin, at the doses tested, was without effect on avoidance conditioning but produced decreased locomotion. These data suggest that the tyrosine end of the enkephalin molecule may be important for its effects on conditioning. Because of their low opioid potencies, it is unlikely that the behavioral actions of tyr-gly-gly and des-tyr-[leu]enkephalin are mediated through opioid receptors. 相似文献
5.
Hydrolysis of [Leu]- and [Met]enkephalin was determined in whole rat plasma in vitro by using HPLC-ECD to measure Tyr, Tyr-Gly and Tyr-Gly-Gly formation. Although [Leu]- and [Met]enkephalin did not differ in Tyr or Tyr-Gly accumulation, the amount of Tyr-Gly-Gly resulting from [Met]enkephalin hydrolysis was greater than that resulting from [Leu]enkephalin hydrolysis, and [Met]enkephalin's half-life in plasma was slightly shorter than that of [Leu]enkephalin. By comparing metabolite formation in the presence and absence of peptidase inhibitors with high selectivity for their respective enzymes, these studies demonstrated that aminopeptidase M and angiotensin converting enzyme are the major peptidases that hydrolyze enkephalins in rat plasma. 相似文献
6.
V Duprez R Maziarz O Weinberger S J Burakoff 《Journal of immunology (Baltimore, Md. : 1950)》1984,132(5):2185-2189
A model system has been developed to study extrathymic T cell differentiation; mice have been thymectomized, lethally irradiated, and reconstituted with bone marrow cells depleted of Thy-1+ cells. After 8 wk, the spleen cells of these athymic, bone marrow-reconstituted chimeras contain Thy-1+ precytolytic T lymphocytes (CTL) that are able to respond to antigen only if supernatant from Con A-activated T cells is added to culture. The phenotype of these pre-CTL is similar to that of thymocytes, suggesting that they may be immature T cells. Initial evaluation of the CTL repertoire of these athymic mice demonstrated that the CTL generated to trinitrophenyl-modified syngeneic cells are H-2-restricted, and that the CTL generated to alloantigens have many of the cross-reactivities observed in normal mice but not in nude mice. In this report, we demonstrate a helper T cell defect in these thymectomized chimeras. These chimeras lack an Ly-1+ helper cell required for thymocytes to differentiate to CTL. Further studies revealed that when spleen cells from these thymectomized chimeras were stimulated with Con A, they produced normal levels of interleukin 2. However, these splenocytes were defective in the production of another factor needed for CTL differentiation. 相似文献
7.
J. A. P. Rostas V. A. Brent J. W. Heath R. L. B. Neame D. A. Powis R. P. Weinberger P. R. Dunkley 《Neurochemical research》1986,11(2):253-268
Incubation of subcellular fractions isolated from rat cerebral cortex with [-32P]ATP results in the phosphorylation of a number of proteins including two with apparent molecular weights of approximately 50,000 and 60,000 daltons. These phosphoproteins were shown to be the autophosphorylated subunits of a calmodulin-stimulated protein kinase by a number of physicochemical criteria, including their mobility on non-equilibrium pH gradient electrophoresis, their phosphopeptide profiles and phosphorylation characteristics. When a crude membrane fraction obtained following osmotic lysis of a P2 fraction was labeled and subsequently fractionated on sucrose density gradients, approximately 80% of the autophosphorylated kinase was associated with fractions enriched in synaptic plasma membranes. Other substrates of calmodulin kinase(s) were similarly distributed. Detergent extraction of synaptic plasma membranes to produce synaptic junctions and post-synaptic densities indicated that the majority of the autophosphorylated kinase was solubilized, apparently as a holoenzyme. The major post synaptic density protein (mPSDp) was not readily extracted by detergents and was largely unlabeled under the conditions used for phosphorylation, and yet this protein is structurally closely related to the kinase subunit. It is possible that this lack of labeling is due to the mPSDp being attached to the PSD in a different way or being present there in a different isoenzymic form from that of the readily autophosphorylated enzyme subunit. Thus, the data suggest that, in vitro at least, a number of pools of calmodulin kinase exist in neuronal membranes.A preliminary account of part of this work has been published (1). 相似文献
8.
The Drosophila melanogaster gene flightless-I, involved in gastrulation and
muscle degeneration, has Caenorhabditis elegans and human homologues. In
these highly conserved genes, two previously known gene families have been
brought together, families encoding the actin- binding proteins related to
gelsolin and the leucine-rich-repeat (LRR) group of proteins involved in
protein-protein interactions. Both these gene families exhibit
characteristics of molecular changes involving replication slippage and
exon shuffling. Phylogenetic analyses of 19 amino acid sequences of 6
related protein types indicate that actin- associated proteins related to
gelsolin are monophyletic to a common ancestor and include flightless
proteins. Conversely, comparison of 24 amino acid sequences of LRR proteins
including the flightless proteins indicates that flightless proteins are
members of a structurally related subgroup. Included in the flightless
cluster are human and mouse rsp-1 proteins involved in suppressing v-Ras
transformation of cells and the membrane-associated yeast (Saccharomyces
cerevisae) adenylate cyclase whose analogous LRRs are required for
interaction with Ras proteins. There is a strong possibility that ligands
for this group could be related and that flightless may have a similar role
in Ras signal transduction. It is hypothesized that an ancestral monomeric
gelsolin precursor protein has undergone at least four independent gene
reorganization events to account for the structural diversity of the extant
family of gelsolin-related proteins and that gene duplication and exon
shuffling events occurred prior to or at the beginning of multicellular
life, resulting in the evolution of some members of the family soon after
the appearance of actin-type proteins.
相似文献
9.
Three species of the genus Arthrobacter, A. crystallopoietes, A. pyridinolis, and A. viridescens, have the capabilities to utilize 2-hydroxypyridine (2-HP) as the sole source of carbon and nitrogen for growth and to produce an extracellular crystalline pigment from this substrate. Degradation of 2-HP by cell-free extracts requires the presence of both reduced nicotinamide adenine dinucleotide and molecular oxygen and is stimulated by flavin mononucleotide, suggesting the presence of a monooxygenase activity in the extract. Loss of the ability to produce pigment at a high spontaneous frequency, 0.26% loss per generation, is observed only with A. crystallopoietes and can be visualized by the presence of sectored and fully nonpigmented colonies on solid media containing 2-HP. Concomitant with the loss of pigment-producing character are both loss of ability to utilize 2-HP for growth and oxidation of 2-HP by cell-free extracts. These three 2-HP-associated characteristics also are lost simultaneously by treating cultures of A. crystallopoietes with curing agents, such as acridine orange and mitomycin C, but are not curable in A. pyridinolis or A. viridescens. All nonpigmented strains of A. crystallopoietes are nonrevertible for these properties. These data suggest that 2-HP-related characteristics are plasmid determined in A. crystallopoietes but not in A. pyridinolis and A. viridescens. A survey for the presence of plasmids in these three species and two physiologically unrelated species, A. globiformis and A. atrocyaneus, revealed plasmid material only in A. globiformis and A. crystallopoietes. 相似文献
10.
Nuclear acceptor sites for androgen-receptor complexes in seminal-vesicle epithelium. 总被引:1,自引:1,他引:0
An assay method in vitro was developed and applied to quantify acceptor binding of steroid-receptor complexes in nuclei from isolated epithelium of guinea-pig seminal vesicle. Steroid-receptor complex prepared from 1-day-castrated animals was incubated with purified nuclei from 1-28 day-castrated animals in a medium containing 0.15 M-KCl. Free and bound steroid-receptor complexes were measured and the data were submitted to Scatchard analysis. With nuclei from 1-day-castrated animals the Kd for binding of cytosolic [3H]dihydrotestosterone-receptor complexes was found to be 0.83 X 10(-10) M and the capacity for binding was 0.35 pmol/mg of nuclear DNA. Scatchard analysis consistently disclosed only a single line of constant slope and gave the same kinetic constants for nuclei obtained from animals castrated up to 28 days before assay. Administration of 2 mg of dihydrotestosterone, 3 alpha-androstanediol or androsterone or 100 microgram of oestradiol-17 beta 1 h before killing of the 1-day-castrated animals that provided the nuclei resulted in a significant decrease in nuclear acceptor binding of the steroid-receptor complex compared with untreated animals. Thus our assay method disclosed nuclear acceptor sites that may be involved in responses to androgens (and oestrogens) in vivo. We conclude that there is a class of nuclear accept or sites of high affinity and limited capacity that may be occupied by steroid-receptor complexes in vivo. 相似文献