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991.
The bacteriophage T4 gene for the small subunit of ribonucleotide reductase contains an intron. 总被引:21,自引:3,他引:21 下载免费PDF全文
The bacteriophage T4 gene nrdB codes for the small subunit of the enzyme ribonucleotide reductase. The T4 nrdB gene was localized between 136.1 kb and 137.8 kb in the T4 genetic map according to the deduced structural homology of the protein to the amino acid sequence of its bacterial counterpart, the B2 subunit of Escherichia coli. This positions the C-terminal end of the T4 nrdB gene approximately 2 kb closer to the T4 gene 63 than earlier anticipated from genetic recombinational analyses. The most surprising feature of the T4 nrdB gene is the presence of an approximately 625 bp intron which divides the structural gene into two parts. This is the second example of a prokaryotic structural gene with an intron. The first prokaryotic intron was reported in the nearby td gene, coding for the bacteriophage T4-specific thymidylate synthase enzyme. The nucleotide sequence at the exon-intron junctions of the T4 nrdB gene is similar to that of the junctions of the T4 td gene: the anticipated exon-intron boundary at the donor site ends with a TAA stop codon and there is an ATG start codon at the putative downstream intron-exon boundary of the acceptor site. In the course of this work the denA gene of T4 (endonuclease II) was also located. 相似文献
992.
F Z Stanczyk D L Hess P C Namkung J W Senner P H Petra M J Novy 《Biology of reproduction》1986,35(1):126-132
Temporal relationships between concentrations of sex steroid-binding protein (SBP), corticosteroid-binding globulin (CBG), total and free estradiol, total and free testosterone, cortisol, and progesterone were studied in plasma obtained at 1- to 3-day intervals throughout gestation in six rhesus macaques. Concentrations of SBP and CBG were measured by diethylaminoethyl cellulose filter assays. Total and free steroids were estimated by radioimmunoassay and ultrafiltration dialysis, respectively. We found that SBP was elevated between days 30 and 50 and CBG between days 60 and 140; both then declined until term (167 days). Estradiol increased gradually throughout gestation. Testosterone was elevated between days 10 and 40, then declined, and rose slightly in late gestation until approximately 15 days before delivery, when it increased markedly. Free estradiol and testosterone increased dramatically before parturition. Progesterone was elevated between days 25 and 45 and declined to relatively constant levels thereafter. Cortisol was essentially unchanged throughout gestation. Our data show that in the pregnant rhesus, levels of SBP and CBG vary independently of one another, but both decline before term; concentrations of both total and free estradiol and testosterone increase markedly before parturition; in late gestation, elevated estrogen is not associated with increased levels of SBP or CBG (as it is in human females). 相似文献
993.
The membrane phospholipid and fatty acid compositions of Mycoplasma hyopneumoniae, a pathogen of porcine enzootic pneumoniae isolated in China, was studied by thin-layer chromatography and gas chromatography. The results showed that membrane phospholipids consisted predominantly of diphosphatidylglycerol. The percentage of C16 - C18 fatty acids comprised 79% of the total fatty acids, of which oleic acid as well as palmitic acid are the major fatty acids. Some differences were shown in fatty acid composition as compared with membranes of other species of Mycoplasma. 相似文献
994.
J H Kim H J Do W H Wang Z Macháty Y M Han B N Day R S Prather 《Biology of reproduction》1999,61(4):900-905
This study was conducted to determine whether a protein tyrosine kinase (PTK) activity is involved in the initiation of the events that occur at fertilization in pig oocytes. After maturation for 47 h, a 7-h treatment of oocytes with 1 mM sodium orthovanadate, which is an inhibitor of protein tyrosine phosphatase, caused more than 90% pronuclear formation, cortical granule exocytosis, and a decrease in mitogen-activated protein kinase activity. Immunoblotting with an antibody specific for phosphotyrosine showed at least three proteins whose phosphotyrosine contents were significantly increased upon treatment of oocytes with 1 mM sodium orthovanadate. Preincubation of pig oocytes with 50 microM tyrphostin 47, a specific PTK inhibitor, completely blocked the ability of sodium orthovanadate to trigger activation events. In addition, when oocytes were pretreated with the calcium-chelating agent BAPTA-AM, sodium orthovanadate-stimulated pronuclear formation was significantly (P < 0.01) reduced (94.0% vs. 43.1%). These results suggest that PTK may be involved in pig oocyte activation in a calcium-dependent manner and that the stimulation of tyrosine kinase is able to signal a series of intracellular changes that lead to the activation events associated with fertilization. 相似文献
995.
低分子抑瘤物净化白血病细胞的实验研究及临床应用 总被引:3,自引:0,他引:3
胎儿肝脏中存在一类小分子量(分子量〈10kD)的肿瘤抑制物,其在体外对HL-60等多种白血病细胞系具有明显的选择性抑制作用,对急性白血病患者骨髓的白血病祖细胞也具有这种选择性抑制效果;分离纯化获得两种天然低分子抑瘤物(7-KC和7-β-HC)和一种外源性低分子抑瘤物(DBP),研究证实其抑制白血病细胞生长的作用机制是诱导白血病细胞凋亡;将其应用于白血病及恶性淋巴瘤自体骨髓移植时的体外净化,完成12 相似文献
996.
Shum PW Peet NP Weintraub PM Le TB Zhao Z Barbone F Cashman B Tsay J Dwyer S Loos PC Powers EA Kropp K Wright PS Bitonti A Dumont J Borcherding DR 《Nucleosides, nucleotides & nucleic acids》2001,20(4-7):1067-1078
Cyclin-dependent kinases (CDKs) belong to a class of enzymes that control the ability of a cell to enter into and proceed through the cell division cycle. Using purine as a scaffold, we have synthesized a number of nanomolar inhibitors of CDK-2/cyclin E. In this report, the synthesis of a series of piperidine-substituted purine analogs will be presented, as well as some of their in vitro and in vivo biological effects. 相似文献
997.
Yang Y Cheng JZ Singhal SS Saini M Pandya U Awasthi S Awasthi YC 《The Journal of biological chemistry》2001,276(22):19220-19230
The physiological significance of the selenium-independent glutathione peroxidase (GPx) activity of glutathione S-transferases (GSTs), associated with the major Alpha class isoenzymes hGSTA1-1 and hGSTA2-2, is not known. In the present studies we demonstrate that these isoenzymes show high GPx activity toward phospholipid hydroperoxides (PL-OOH) and they can catalyze GSH-dependent reduction of PL-OOH in situ in biological membranes. A major portion of GPx activity of human liver and testis toward phosphatidylcholine hydroperoxide (PC-OOH) is contributed by the Alpha class GSTs. Overexpression of hGSTA2-2 in K562 cells attenuates lipid peroxidation under normal conditions as well as during the oxidative stress and confers about 1.5-fold resistance to these cells from H(2)O(2) cytotoxicity. Treatment with 30 microm H(2)O(2) for 48 h or 40 microm PC-OOH for 8 h causes apoptosis in control cells, whereas hGSTA2-2-overexpressing cells are protected from apoptosis under these conditions. In control cells, H(2)O(2) treatment causes an early (within 2 h), robust, and persistent (at least 24 h) activation of JNK, whereas in hGSTA2-2-overexpressing cells, only a slight activation of JNK activity is observed at 6 h which declines to basal levels within 24 h. Caspase 3-mediated poly(ADP-ribose) polymerase cleavage is also inhibited in cells overexpressing hGSTA2-2. hGSTA2 transfection does not affect the function of antioxidant enzymes including GPx activity toward H(2)O(2) suggesting that the Alpha class GSTs play an important role in regulation of the intracellular concentrations of the lipid peroxidation products that may be involved in the signaling mechanisms of apoptosis. 相似文献
998.
Mycotoxin production from fungi isolated from grapes 总被引:6,自引:0,他引:6
Abrunhosa L Paterson RR Kozakiewicz Z Lima N Venâncio A 《Letters in applied microbiology》2001,32(4):240-242
AIMS: In order to assess the potential for producing mycotoxins, fungi were isolated from wine producing grapes. METHODS AND RESULTS: The isolates were identified and Penicillium expansum, the most well recognized mycotoxin producer, was analysed for mycotoxin production by TLC. Many of the strains produced patulin and/or citrinin, often depending on whether they were grown on a grape or yeast extract sucrose media. CONCLUSION: Citrinin was produced by all strains grown in the yeast extract sucrose medium, but only one strain (from 51) was able to produce this compound in grape juice medium. Patulin was produced in the yeast extract medium by 20 strains and in grape juice medium by 33 strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of mycotoxins in wine producing grapes is discussed. Grapes contamination with patulin seems not to contribute to wine contamination, and no ochratoxin producing fungi was identified. 相似文献
999.
Epidermal growth factor-induced tumor cell invasion and metastasis initiated by dephosphorylation and downregulation of focal adhesion kinase 总被引:18,自引:0,他引:18 下载免费PDF全文
Upregulated epidermal growth factor (EGF) receptor (EGFR) expression and EGFR-induced signaling have been correlated with progression to invasion and metastasis in a wide variety of carcinomas, but the mechanism behind this is not well understood. We show here that, in various human carcinoma cells that overexpress EGFR, EGF treatment induced rapid tyrosine dephosphorylation of focal adhesion kinase (FAK) associated with downregulation of its kinase activity. The downregulation of FAK activity was both required and sufficient for EGF-induced refractile morphological changes, detachment of cells from the extracellular matrix, and increased tumor cell motility, invasion, and metastasis. Tumor cells with downregulated FAK activity became less adherent to the extracellular matrix. However, once cells started reattaching, FAK activity was restored by activated integrin signaling. Moreover, this process of readhesion and spreading could not be abrogated by further EGF stimulation. Interruption of transforming growth factor alpha-EGFR autocrine regulation with an EGFR tyrosine kinase inhibitor led to a substantial increase in FAK tyrosine phosphorylation and inhibition of tumor cell invasion in vitro. Consistent with this, FAK tyrosine phosphorylation was reduced in cells from tumors growing in transplanted, athymic, nude mice, which have an intact autocrine regulation of the EGFR. We suggest that the dynamic regulation of FAK activity, initiated by EGF-induced downregulation of FAK leading to cell detachment and increased motility and invasion, followed by integrin-dependent reactivation during readhesion, plays a role in EGF-associated tumor invasion and metastasis. 相似文献
1000.