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Biomedical subjects

G Milman

Publications and source records attributed to G Milman.

At least 37 records · Page 2Linked to original sources
PubMed1985

A second Epstein-Barr virus early antigen gene in BamHI fragment M encodes a 48- to 50-kilodalton nuclear protein.

We used antiserum raised against the bacterially synthesized product of one of the open reading frames in Epstein-Barr virus (EBV) BamHI fragment M to demonstrate that this reading frame (BMRF1) codes for a nuclear protein of the diffuse early antigen (EA) class. In indirect immunofluorescence assays, the rabbit anti-BMRF1 antiserum gave nuclear staining in approximately 5% of Raji cells which had been treated with sodium butyrate, and positive fluorescence was observed in both acetone- and methanol-fixed cells. Uninduced Raji cultures contained less than 0.1% positive cells regardless of whether indirect immunofluorescence or anti-complement immunofluorescence was used. In immunoblot analyses, the rabbit serum identified a family of polypeptides of 46 to 55 kilodaltons (kDa) in total protein extracts from B95-8 cells or from butyrate-induced Raji cells. In both cell types, the dominant polypeptides were the 48- and 50-kDa species. This same family of polypeptides was identified when the immunoblots were reacted with the R3 monoclonal antibody, and we concluded that this antibody also recognized the product of the BMRF1 open reading frame. Fibroblast cell lines containing EBV BamHI fragment M were established by cotransfection of baby hamster kidney cells with BamHI-M and the gene for neomycin resistance. Aminoglycoside G418-resistant colonies which showed evidence for EBV antigen expression in immunofluorescence assays were selected, and clonal cell lines were established. After 3 to 4 months of passaging, constitutive synthesis of EA was no longer detectable in these cell lines either by immunofluorescence or by immunoblot analysis. However, in the one cell line examined, synthesis of the 48- to 50-kDa EA was induced by treatment of the culture with sodium butyrate. Thus, the regulation of expression of this EA in transfected fibroblasts is analogous to that seen in Raji lymphoblasts. We showed previously that BamHI fragment M also contains the coding sequences for a 60-kDa nuclear EA, and hence BamHI-M encodes two separate components of the diffuse EA complex.

Antibodies, Monoclonal↗
PubMed1984

Short-term, high-efficiency expression of transfected DNA.

We have achieved high-efficiency uptake and expression of foreign DNA in mouse Ltk- cells by modifying the DEAE-dextran-mediated transfection method of McCutchan and Pagano (J. Natl. Cancer Inst. 42:351-357, 1968) to include an initial incubation at elevated pH followed by a shock treatment with dimethyl sulfoxide. Up to 80% of mouse Ltk- cells transfected with the herpes simplex virus thymidine kinase gene expressed thymidine kinase as measured by autoradiography.

Animals↗
PubMed1984

Transfer of herpes simplex virus thymidine kinase synthesized in bacteria by a high-expression plasmid to tissue culture cells by protoplast fusion.

The introduction of a protein into living tissue culture cells may permit the in vivo study of functions of the protein. We have previously described a high-efficiency-expression plasmid, pHETK2, containing the herpes simplex virus type 1 thymidine kinase (TK) gene which, upon temperature induction, causes TK to be synthesized as greater than 4% of the bacterial protein. In this report we show that enzymatically active TK was transferred to mouse Ltk- cells by polyethylene glycol-mediated fusion with protoplasts prepared from bacteria containing induced levels of TK. The presence of TK in the Ltk- cells was detected by the incorporation of [3H]thymidine into cell nuclei as measured by autoradiography.

Animals↗
PubMed1983

Purification and characterization of herpes simplex virus (type 1) thymidine kinase produced in Escherichia coli by a high efficiency expression plasmid utilizing a lambda PL promoter and cI857 temperature-sensitive repressor.

The structural gene for herpes simplex virus (type 1) thymidine kinase was cloned downstream from the lambda phage high efficiency leftward promotor in a plasmid (pHETK2) also containing the gene for the lambda cI857 temperature-sensitive repressor. Thymidine kinase is synthesized as a run-on product containing the NH2 terminus of the lambda N protein. Heat inactivation of the lambda repressor by growth at 42 degrees C results in the accumulation of thymidine kinase as approximately 4% of the total soluble cellular protein. Thymidine kinase has been purified to greater than 95% homogeneity by high speed centrifugation, ammonium sulfate fractionation, and Sephadex G-100 and hydroxylapatite column chromatography. Thymidine kinase has a subunit Mr = 42,000 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and behaves as a dimer during Sephadex G-100 chromatography and glycerol gradient centrifugation. Thymidine kinase is enzymatically active from pH 6 to 10 with maximum activity at pH 8.5. The enzyme is protected from heat inactivation by thymidine and has a half-life at 40 degrees C of 30 min in the presence of thymidine and 3 min in its absence. Thymidine kinase displays Michaelis-Menten kinetics with apparent Michaelis constants of 0.6 and 118 microM for thymidine and ATP, respectively. Iododeoxycytidine is a competitive inhibitor of thymidine with an apparent Ki of 14 microM. The anti-herpes drug acyclovir (9-[(2-hydroxyethoxy)methyl]guanine) also appears to be a competitive inhibitor of thymidine (Ki of approximately 300 microM) but requires 3,000-fold higher concentrations than thymidine to give 50% inhibition. Other nucleoside triphosphates can substitute for ATP in the kinase reaction with the exception of dTTP which appears to inhibit thymidine kinase activity by about 50% when present in concentrations equal to that of thymidine.

Bacteriophage lambda↗
PubMed1983

Purification and characterization of Escherichia coli guanine-xanthine phosphoribosyltransferase produced by a high efficiency expression plasmid utilizing a lambda PL promoter and CI857 temperature-sensitive repressor.

The gene for Escherichia coli guanine-xanthine phosphoribosyltransferase was placed after the high efficiency lambda phage leftward promoter in plasmid pHEGPT also containing the lambda CI857 temperature-sensitive repressor. Guanine-xanthine phosphoribosyltransferase increases 780-fold when cells containing pHEGPT are shifted from 30 to 42 degrees C. Guanine-xanthine phosphoribosyltransferase represents approximately 5% of the protein in a crude extract of induced cells. Guanine-xanthine phosphoribosyltransferase may be purified to apparent homogeneity by ammonium sulfate fractionation, Sephadex G-100, and DEAE-cellulose column chromatography. The enzyme has a subunit molecular weight of 18,600 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and behaves as a trimer during Sephadex G-100 column chromatography. Guanine-xanthine phosphoribosyltransferase is active from pH 7.5 to 10.5 with maximum activity at pH 9.5. The enzyme is protected from heat inactivation by phosphoribosylpyrophosphate (PRPP). At 65 degrees C, the enzyme has a half-life of 2 min in the absence of PRPP and 90 min in the presence of PRPP. The enzyme displays Michaelis-Menten kinetics with apparent Michaelis constants for guanine, xanthine, hypoxanthine, and PRPP of 2.6, 39, 167, and 95 microM, respectively. The activity of the enzyme with guanine is 2-fold greater than that with xanthine and 3-fold greater than that with hypoxanthine.

DNA Restriction Enzymes↗
PubMed1982

Encapsidation and expression of the herpes thymidine kinase gene in polyoma virus.

A recombinant DNA of 5,150 base pairs was prepared containing the intact early region of polyoma virus, including the viral origin of replication and the structural sequences of the herpes simplex virus type 1 thymidine kinase gene. Although no thymidine kinase activity was detected when herpes structural sequences alone were transfected into cells, activity was produced when the structural gene followed the polyoma early region. The recombinant DNA was encapsidated into polyoma virions when cotransfected into mouse 3T6 cells with helper DNA from an early polyoma virus mutant. Herpes thymidine kinase activity was detected by a rapid in situ autoradiographic assay in which [125]iododeoxycytidine was utilized as a substrate for the viral but not the cellular enzyme.

Animals↗
PubMed1982

Viable polyoma virus with four BamHI decanucleotide linkers inserted at the 26-minute HincII site.

BamHI decanucleotide linkers (5' CCGGATCCGG 3') were ligated to full-length linear polyoma DNA partially cleaved with HincII, and the recombinant DNA was transfected into mouse 3T6 cells. A viable virus (PYNB5) was isolated which contains four linkers at the 26-min HincII site. PYNB5 is encapsidated with a larger major viral capsid protein (VP1) as predicted from the DNA sequence. PYNB5 appears to have the same growth and physical properties as the wild-type virus with the exception of greater inactivation upon dilution of virus stocks with water. When PYNB5 DNA is cleaved with BamHI, the larger of the two resulting fragments (PY66) contains an intact early region of the virus, including the origin of DNA replication. PY66 complements a polyoma early region mutant for growth and may be useful as a cloning vector for foreign DNA.

Animals↗
PubMed1981

Efficient DNA transfection and rapid assay for thymidine kinase activity and viral antigenic determinants.

We describe DEAE dextran-mediated DNA transfection in suspension which routinely gives transient gene expression in 0.1--1% of the transfected cells. We have used normal diploid human skin fibroblasts, monkey BSC cells, and mouse L or 3T6 cells with almost equal efficiency. Gene expression is detected 1--3 days after addition of the DNA. SV40 and polyoma T and V antigen are detected by in situ immunofluorescence and thymidine kinase gene expression is detected by in situ autoradiography. The high efficiency of transfection and the speed of detection together provide a means to study transfecting gene functions that does not rely on selection to obtain stable transformants. It should be possible to screen for the expression of any gene product which can be assayed by in situ immunofluorescence or autoradiographic techniques.

Animals↗
PubMed1979

Analysis of HGPRT- CRM+ human lymphoblast mutants.

Three 6-thioguanine-resistant mutants of the human diploid lymphoblast line MGL-8 were studied. The inactivation by heat of both HGPRT activity and antigenicity of the HGPRT immunologically cross-reacting material of the A30 mutant cells were not protected by PRPP, indicating that the HGPRT in A30 cells has an altered PRPP binding site, leading to lack of stabilization and rapid degradation of the enzyme. Two dimensional separations of the immunoprecipitates from extracts of the parental and mutant cell lines showed that the A35 mutant CRM has a more acidic isoelectric pH, while the A30 CRM has a more basic isoelectric pH and that the A30 protein has a faster rate of degradation than the wild-type HGPRT. The A30 CRM also has a smaller molecular size than the wild-type enzyme.

Cell Line↗
PubMed1977

Hypoxanthine phosphoribosyltransferase: two-dimensional gels from normal and Lesch-Nyhan hemolyzates.

Immunoprecipitated hypoxanthine phosphoribosyltransferase (HPRT) from hemolyzates displays two major spots after two-dimensional polyacrylamide gel electrophoresis. HeLa cells or human lymphoblasts display only a single HPRT spot located at the same position as the most basic of the hemolyzate HPRT spots. This suggests that the most basic spot is the form initially synthesized, and the more acidic hemolyzate HPRT spot (a pseudoisozyme) is probably derived from the first by an age-related modification (for example, deamidation). The HPRT pattern of the hemolyzate from a Lesch-Nyhan patient was shifted to a more basic isoelectric pH, implying the mutation of a structural gene.

Chemical Precipitation↗
PubMed1977

Human hypoxanthine phosphoribosyltransferase. Purification and properties.

Hypoxanthine phosphoribosyltransferase (IMP:pryophosphate phosphoribosyltransferase, EC 2.4.2.8) from human erythrocytes has been purified 13 000-fold to apparent homogeneity. The native enzyme has a sedimentation coefficient of 5.9 S, determined by analytical ultracentrifugation, and a molecular weight of 81 000-83 000, determined by sedimentation equilibrium centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a subunit molecular weight of 26 000, suggesting that the enzyme is a trimer. Isoelectric focusing resolves three peaks of enzyme activity at pH 5.6, 5.7 and 5.9. The amino acid composition of hypoxanthine phosphoribosyltrasferase is 17 Lys, 5 His, 12 Arg, 0 Trp, 31 Asx, 12 Thr, 14 Ser, 16 Glx, 14 Pro, 19 Gly, 12 Ala, 5 Cys, 18 Val, 5 Met, 11 Ile, 20 Leu, 10 Tyr, and 9 Phe. The enzyme appears to have a blocked N terminus.

Amino Acid Sequence↗
PubMed1977

Tryptic peptide analysis of normal and mutant forms of hypoxanthine phosphoribosyltransferase from HeLa cells.

Hypoxanthine phosphoribosyltransferase (HPRT, IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) can be purified 5-to 10,000-fold from extracts of HeLa (human) cells by a three-step procedure consisting of high-speed centrifugation, adsorption to Sepharose-conjugated HPRT antibody, and sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Purified enzyme labeled in vivo with radioactive lysine, arginine, or methionine was digested with trypsin and the tryptic peptides were separated by column chromatography on Bio-Rad cation exchanger Aminex A-5. Less than 50 ng (2 pmol) of HPRT is required to produce a tryptic peptide pattern. A methionine-labeled peptide was identified as the COOH-terminus because it was not labeled with either lysine or arginine. We have compared the tryptic peptide patterns of normal HeLaHPRT and a crossreacting HPRT protein lacking enzyme activity from HeLa mutant H23 [Milman et al. (1976) Proc. Natl. Acad. Sci. USA 73, 4589--4593]. The mutant protein has a new lysine-labeled peptide, but the chromatography patterns of arginine- or methionine-labeled peptides appear identical to those of the normal protein. The appearance in the H23 mutant HPRT protein of a new tryptic peptide provides strong evidence for a mutation in the HPRT structural gene. The tryptic peptide patterns were used to determine the total number of residues of labeled amino acid in the protein, and the values are reasonably consistent with those determined by conventional amino acid analysis pf erythrocyte HPRT.

HeLa Cells↗
PubMed1976

Chinese hamster purine-nucleoside phosphorylase: purification, structural, and catalytic properties.

Purine-nucleoside phosphorylase (EC 2.4.2.1; purine-nucleosideorthophosphate ribosyltransferase) was purified to apparent homogeneity from Chinese hamster liver and kidneys and from V79 tissue culture cells. The enzymes from both sources appear to have identical structural and catalytic properties. A simple rapid radioisotope assay capable of detecting 0.1 nmol of product for both directions of the purine-nucleoside phosphorylase reaction is described using Bio-Rad Cu2+ Chelex in Pasteur pipet columns. At 37 degrees C the purified enzyme converts 60 mumol of guanine to guanosine per min per mg of protein. Electrophoresis in sodium dodecyl sulfate-polyacrylamide gels indicates that the enzyme is composed of identical subunits of 30 000 molecular weight. The native enzyme behaves as a mixture of dimers of 68 000 molecular weight and trimers of 89 000 molecular weight during Sephadex G-100 chromatography. Sucrose gradient centrifugation indicates that the enzyme had a sedimentation coefficient of 5.4 S, which corresponds to a molecular weight of 94 000 and suggests a trimer structure. The enzyme displays Michaelis-Menten kinetics with apparent Michaelis constants of 20 muM both hypoxanthine and guanine, 35 muM form guanosine, 50 muM for inosine, and 200 muM for both ribose 1-phosphate and phosphate. During isoelectrofocusing, the enzyme forms a single major band at a pI of 5.25.

Animals↗