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1.
Genetic and Physical Mapping of the Mcra (Rgla) and Mcrb (Rglb) Loci of Escherichia Coli K-12 总被引:17,自引:1,他引:16 下载免费PDF全文
We have genetically analyzed, cloned and physically mapped the modified cytosine-specific restriction determinants mcrA (rglA) and mcrB (rglB) of Escherichia coli K-12. The independently discovered Rgl and Mcr restriction systems are shown to be identical by three criteria: 1) mutants with the RglA- or RglB- phenotypes display the corresponding McrA- or McrB- phenotypes, and vice versa; 2) the gene(s) for RglA and McrA reside together at one locus, while gene(s) for RglB and McrB are coincident at a different locus; and 3) RglA+ and RglB+ recombinant clones complement for the corresponding Mcr-deficient lesions. The mcrA (rglA) gene(s) is on the excisable element e14, just clockwise of purB at 25 min. The mcrB (rglB) gene(s), at 99 min, is in a cluster of restriction functions that includes hsd and mrr, determinants of host-specific restriction (EcoK) and methyladenine-specific restriction respectively. Gene order is mcrB-hsdS-hsdM-hsdR-mrr-serB. Possible models for the acqusition of these restriction determinants by enteric bacteria are discussed. 相似文献
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Gamma-T4 hybrid bacteriophage carrying the thymidine kinase gene of bacteriophage T4. 总被引:3,自引:1,他引:2 下载免费PDF全文
Among 32 lambda-T4 recombinant phages selected for growth on a thymidylate synthetase-deficient (thyA) host, 2 were shown to carry the T4 thymidine kinase (tk) gene. The lambda-T4tk phages contain two T4 HindIII DNA fragments (2.0 and 1.5 kilobases) that hybridize to restriction fragments of T4 DNA, encompassing the tk locus at 60 kilobases on the T4 map. The T4tk insert compensates for the simultaneous host deficiencies of thymidine kinase and thymidylate synthetase in a thymidine kinase-deficient (tdk) host growing in the presence of fluorodeoxyuridine when provided with thymidine and uridine. The lambda-T4tk hybrid phages specified five polypeptides with Mrs of 22,000 (22K), 21K, 14K, 11K, and 9K. 相似文献
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Human interferons-alpha, -beta and -gamma enhance HLA-DR mRNAs in all the human lymphoblastoid and melanoma cell lines studied. The increase concerns both alpha and beta chain mRNAs. Moreover, we show that immune interferon-gamma preferentially enhances class II MHC mRNA. This effect of IFN-gamma on the synthesis of alpha and beta HLA-DR chains has been also analysed by immunoprecipitation. It is abolished by a monoclonal antibody directed against human IFN-gamma. The effect of interferon on the cell surface level of HLA-DR molecules does not always correspond to the enhancement of HLA-DR mRNA. Our experiments suggest that this discrepancy between the enhancement of HLA-DR mRNA and cell surface antigen might be due to a constitutively high level of the corresponding antigens on several of the human cells studied. 相似文献
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Interferon-induced 56,000 Mr protein and its mRNA in human cells: molecular cloning and partial sequence of the cDNA. 总被引:25,自引:2,他引:23 下载免费PDF全文
Treatment of responsive cells by interferons (IFNs) induces within a few hours a rise in the concentration of several proteins and mRNAs. In order to characterize these IFN-induced mRNA species, we have cloned in E. coli the cDNA made from a 17-18S poly(A)+ RNA of human fibroblastoid cells (SV80) treated with IFN-beta. We describe here a pBR322 recombinant plasmid (C56) which contains a 400 bp cDNA insert corresponding to a 18S mRNA species newly induced by IFN. The C56 mRNA codes for a 56,000 dalton protein easily detectable by hybridization-translation experiments. The sequence of 66 of the carboxy-terminal amino-acids of the protein can be deduced from the cDNA sequence. IFNs-alpha, beta or gamma are able to activate the expression of this gene in human fibroblasts as well as lymphoblastoid cells. The mRNA is not detectable without IFN; it reaches maximum levels (0.1% of the total poly(A)+ RNA) within 4-8 hrs and decreases after 16 hrs. 相似文献
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Differential tyrosine phosphorylation of the IFNAR chain of the type I interferon receptor and of an associated surface protein in response to IFN-alpha and IFN-beta. 总被引:11,自引:3,他引:8 下载免费PDF全文
C Abramovich L M Shulman E Ratovitski S Harroch M Tovey P Eid M Revel 《The EMBO journal》1994,13(24):5871-5877
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THE FINE STRUCTURE OF THE DNP COMPONENT OF THE NUCLEUS : An Electron Microscopic Study Utilizing Autoradiography to Localize DNA Synthesis 总被引:3,自引:13,他引:3 下载免费PDF全文
In the present investigation, the sites of deoxyribonucleic acid (DNA) synthesis and the fate of labeled deoxyribonucleoprotein (DNP) were studied in autoradiographs of ultrathin sections viewed with the electron microscope. Tritiated thymidine was employed as a label for DNA in the nuclei of proliferating cells of regenerating salamander limbs. In the autoradiographic method reported here, dilute NaOH was used to remove the gelatin of the emulsion after exposure and development. The exposed silver grains are not displaced by this treatment and the resolution of fine structure in the underlying section is greatly improved. Our observations suggest that the DNP component is a meshwork of interconnected filaments 50 to 75 A in diameter, which may be cross-linked to form what Frey-Wyssling would term a "reticular gel." The filamentous DNP meshwork is dispersed throughout the interphase nucleus during DNA synthesis, whereas in chromosomes, which are relatively inert metabolically, the meshwork is denser and is aggregated into compact masses. Dense chromatin centers in interphase nuclei are similar in fine structure to chromosomes and are also inert with respect to DNA synthesis. In the Discussion, the structure of the filamentous meshwork in chromatin is compared with that in chromosomes, and speculations are made as to the functional significance of the variations in DNP fine structure observed. 相似文献