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21.
Alternate pathways of DNA replication in Escherichia coli 总被引:2,自引:0,他引:2
We have described the pcbA1 mutation which enables E. coli cells to replicate DNA in the absence of a functional dnaE gene product if DNA polymerase I (the polA gene product) is present. The pcbA1 mutation phenotypically suppresses multiple dnaEts and dnaEam alleles. The pcbA1/PolI replication pathway differs from normal in sensitivity to certain DNA-damaging agents such as methylmethane sulfonate (MMS) and a lack of damage-directed mutagenesis. We report here cloning of the pcbA1 gene in a multicopy plasmid. The pcbA1 mutation is detected only in cis; therefore, cloning necessitated gene eviction. The pcbA1 gene lies closely- linked to gyrB. We have demonstrated the physical presence of DNA polymerase I in the replicating holoenzyme complex by immunoblotting using dnaEam strains. We conclude that E. coli has two alternate replisome structures: REP-A, in which DNA polymerase I is the functional synthetic subunit; and REP-E, in which the alpha-subunit, product of the dnaE gene, is functional. To investigate further the role of individual DNA polymerases in replication, we have isolated the polB gene on multicopy plasmids. 相似文献
22.
Inability of Pseudomonas stutzeri denitrification mutants with the phenotype of Pseudomonas aeruginosa to grow in nitrous oxide. 总被引:8,自引:4,他引:4
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Pseudomonas aeruginosa PAO1 reduced nitrous oxide to dinitrogen but did not grow anaerobically in nitrous oxide. Two transposon insertion Nos- mutants of Pseudomonas stutzeri exhibited the P. aeruginosa phenotype. Growth yield studies demonstrated that nitrous oxide produced in vivo was productively respired, but nitrous oxide supplied exogenously was not. The defect may be in electron transport or in nitrous oxide uptake. 相似文献
23.
Mitogen-like monoclonal anti-actin antibodies 总被引:1,自引:0,他引:1
H M Rosenblatt N Parikh J E McClure I Meza S Y Hwo J Bryan W T Shearer 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(2):995-1000
Monoclonal antibodies (IgM kappa) have been produced to actin isolated electrophoretically from L cell extracts. These monoclonal anti-actin antibodies bind to intact L cells and modulate DNA synthesis and cell proliferation, much like affinity-purified polyclonal rabbit antibody to the same Mr 42,000 actin. In addition, monoclonal antibodies specific for actin from Entamoeba histolytica also bound to and modulated the growth of L cells. A monoclonal antibody directed against a neuroblastoma surface antigen did not produce stimulation of L cells, and the binding activity of anti-actin monoclonal antibody to L cells was removed by absorption with actin covalently coupled to Sepharose. These observations demonstrate the specificity of interaction between the anti-actin monoclonal antibodies and the surface of intact L cells. We conclude that a surface actin-like molecule on the L cell, when bound by specific monoclonal antibody, initiates a stimulatory signal which results in enhanced cellular metabolism. 相似文献
24.
Bryan B. Fuller 《In vitro cellular & developmental biology. Plant》1987,23(9):633-640
Summary Tyrosinase activity increased in Cloudman S-91 mouse melanoma cell homogenates incubated at 37°C for a minimum of 8 h. Enzyme
activity continued to increase for 48h at which time the maximal level of activation was observed. Activation did not occur
at 4°C and did not occur in the cytosol fraction of the cell, suggesting that the response was localized to melanosomes. The
activated enzyme was resistant to solubilization with the nonionic detergent, Triton X-100, and preparation of homogenates
in this detergent did not inhibit the temperature-dependent activation of the melanosomal fraction of the cell. The activation
process increased the V
Max
of tyrosinase 10-fold and lowered the K
M
by a factor of 2 as determined by the tyrosine hydroxylase assay. The increase in tyrosinase activity was detectable by three
assay methods: tyrosine hydroxylation, melanin synthesis, and by tyrosine decarboxylation. The formation of melanin, however,
was found to be 1/20 that of either tyrosine hydroxylation or decarboxylation, a finding which suggests that the melanin pathway
may be blocked at 5,6-dihydroxyindole. The “self-activation” response could not be mimicked by incubating cell homogenates
with cyclic AMP-dependent protein kinase. Activated tyrosinase could be inhibited by the addition of fresh cell extracts,
a finding which suggests that tyrosinase inhibitors may be present in these cells.
This investigation was supported by Public Health Service grants CA41425 and CA30393 awarded by the National Cancer Institute,
Bethesda, MD and by a research grant from the Proctor and Gamble Company. 相似文献
25.
Enhancer sequences responsible for DNase I hypersensitivity in polyomavirus chromatin. 总被引:5,自引:2,他引:3
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DNase I preferentially cleaves polyomavirus minichromosomes at two sites in the enhancer, each of which comprises the sequence AAGCAPuPuAAG flanked by short inverted repeats. A tandem duplication of this sequence generates an additional hypersensitive locus. Mutations which alter either the AAGCAPuPuAAG or flanking repeats diminish hypersensitivity. This region must determine the chromatin conformation recognized by DNase I. 相似文献
26.
Soybean (Glycine max L. Merrill) nodules are usually more enriched in 15N than other tissues. We show that both bacteroids and nodule cortex are considerably more enriched in 15N than nodule cytosol, with bacteroids being slightly more enriched than the cortex. Hence, 15N enrichment occurs in cells of both plant and bacterial origin. 相似文献
27.
Identification and purification of calcium ion dependent modulators of actin polymerization from bovine thyroid 总被引:2,自引:0,他引:2
We describe the purification of Ca2+-dependent actin modulator proteins from bovine thyroid using DNase I affinity chromatography and diethylaminoethylcellulose chromatography. The 40K actin modulator has been purified to 98% homogeneity. It is a single polypeptide chain with a molecular weight of approximately 40 000 and an isoelectric point of 8.1. Its amino acid composition is different from previously described actin-associated proteins and thyroid actin. On the basis of the centrifugation assay and the DNase I inhibition assay, the actin complexed with the 40K protein is G-actin in its conformation rather than F-actin oligomers. Substoichiometric concentrations of the 40K protein rapidly inhibit actin polymerization in the presence of physiological concentrations of Ca2+ and Mg2+. An 80K actin modulator also has been purified to 98% homogeneity. It is a single polypeptide chain with a molecular weight of approximately 80 000 and an isoelectric point of 6.35-7.0. Its amino acid composition is different from those of villin, gelsolin, and leukocyte actin polymerization inhibitor. On the basis of the DNase inhibition assay and the centrifugation assay, the nonprecipitable actin associated with the 80K protein was F-actin in its conformation. The 80K protein acts very efficiently as a Ca2+-dependent nucleator for actin assembly and reduces its viscosity. In addition to the 40K and 80K actin modulators, 91K and 95K actin-associated proteins were partially purified. The 91K-95K fraction has similar activity to the 80K protein regarding precipitation of F-actin. The 125I-G-actin polyacrylamide gel overlay technique [Snabes, M. C., Boyd, A.E., & Bryan, J. (1981) J. Cell Biol. 90, 809-812] revealed that both the 91K and 95K proteins bind 125I-actin after sodium dodecyl sulfate (NaDodSO4) electrophoresis while the 80K and 40K proteins do not. Thyroid 91K protein comigrated with a human platelet 91K actin binding protein on NaDodSO4 gels and may be similar to macrophage gelsolin. The 95K protein may be similar to villin, the intestinal cytoskeletal protein. 相似文献
28.
This paper describes the isolation and amino acid analysis of un-cross-linked elastin obtained by neutral salt extraction from the ligamentum nuchae of a calf fed from birth to 9 months on a diet low in copper. 相似文献
29.
Trisomy 18 associated with a familial translocation t(Bq-; 18q+) 总被引:2,自引:0,他引:2
30.
Synergistic effects of metabolically related amino acids on the growth of a multicellular plant 总被引:2,自引:2,他引:0
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The effects of several amino acids related to the metabolism of aspartic acid on the growth and development of gemmalings of the liverwort Marchantia polymorpha were investigated under axenic conditions. Lysine and theonine synergistically inhibit the growth of these plants and cause a loss of normal pigmentation at concentrations as low as 1 μm. These effects are highly specific for this pair of amino acids, are partially reversible upon removal of the effectors, and can be prevented by low concentrations of methionine or its metabolic precursor, homoserine. Alterations in the growth and development of gemmalings in the presence of natural amino acids are discussed in relation to metabolic regulatory mechanisms which have been well established in microorganisms. 相似文献