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S J O'Brien

Publications and source records attributed to S J O'Brien.

At least 361 records · Page 20Linked to original sources
PubMed1978

Bvr-1, a restriction locus of a type C RNA virus in the feline cellular genome: pleiotropic restriction of endogenous BALB virus in cat X mouse somatic cell hybrids.

Bvr-1 is a dominant X-linked feline gene which restricts the replication of B-tropic murineleukemia virus (B-MuLV) in somatic cell hybrids between murine BALB/c-RAG cells and FL-74 feline cells. Since the hybrids were originally derived by the hypoxanthine aminopterin thymidine selection scheme, counter selection experiments on 6-thioguanine result in preferential survival of hybrid cells which have spontaneously lost the feline X-chromosome on which is located the structural gene for hypoxanthine guanine phosphoribosyl transferase (IMP: pyrophosphate phosphoribosyl transferase, E.C. 2.4.2.8) and Bvr-1. Back selected Bvr-1- cells express high parental levels of B-MuLV. Bvr-1 effectively restricts the IdU-mediated induction of the endogenous xenotropic BALB virus (BALB: virus 2) but not the endogenous N-tropic virus (BALB: virus 1). Pleiotropic restriction of B-MuLV and X-MuLV, but not N-MuLV suggests that the viral targets of Bvr-1 (either viral components or functions in viral assembly) of the B-tropic and X-tropic endogenous BALB viruses are similar to each other but distinct from the target in the N-tropic virus. Very low levels of B-MuLV are detected in restricted cells, but this residual virus is not infectious in either NIH-3T3 or BALB-3T3 mouse cells which are genotypically Fv-1N/Fv-1N and Fv-1B/Fv-1B, respectively. Passage of residual virus through host cells without Fv-1 related restriction (SC-1) results in production of infectious B-MuLV indistinguishable from that produced by RAG parent cells.

Animals↗
PubMed1978

A gene (Bevi) on human chromosome 6 is an integration site for baboon type C DNA provirus in human cells.

Human VA-2 cells infected with baboon type C virus were cloned and fused to Syrian hamster cells, and 33 primary hybrid colonies were obtained. These cells segregated human chromosomes and retained the complete hamster genome. Assays for type C viral p30 antigen and reverse transcriptase were performed in conjunction with analyses of 30 gene-enzyme systems representing 22 different human chromosomes. The results comfirmed that a gene, Bevi, previously assigned to human chromosome 6, dominantly controls baboon type C virus expression in hybrid cells. Representative hybrid colones were studied by nucleic acid hybridization techniques for the presence of integrated proviral DNA using complementary 3H-DNA transcripts of the baboon viral RNA genome. For each of 12 clones examined, there was a concordance between the presence of human chromosome 6, the presence of baboon type C proviral DNA sequences and virus expression. Clones which segregated chromosome 6 as judged by isozyme and karyological analyses lost detectable proviral DNA sequences and failed to produce virus. No syntenic association between the replication of baboon virus and the presence of 21 other human chromosomes was deteced. We conclude that Bevi is a preferred integration site for the baboon type C provirus in the human genome.

Animals↗
PubMed1978

Deposition of retrovirus associated antigens (p30 and gp70) on cell membranes of feline and murine leukaemia virus infected cells.

A quantitative estimation of retrovirus associated cell membrane antigens of murine and feline cells infected with their respective type C leukosis virus is presented. Using a radio-immune assay with three broadly reactive antisera, the minimum estimated number of retrovirus associated antigenic determinants on YAC [Moloney leukaemia virus (MuLV) infected murine] and FL-74 [feline leukaemia virus (FeLV) infected feline] cells was 1.3 x 10(6) and 1.6 x10(6) determinants per cell respectively. The virus structural proteins p27-30 and gp70 were detected by three component specific antisera on murine and feline cell surfaces in amounts which varied between cell isolates. MuLV infected cells produced as many as 1.9 x 10(5) p30 antigenic determinants and 7.5 x 10(5) gp70 determinants on infected cells. FeLV infected cells (FL-74) expressed 5.6 x 10(5) p27 and 7.5 x 10(5) gp70 antigenic determinants per single cell surface. The major core protein (p27-30) and the major envelope glycoprotein (gp70) antigens are sufficiently physically separated on cell surfaces so that binding of either of the membrane antigens with component specific antibodies does not interfere with binding of antibodies specific for the other. Despite the expression of interspecies determinants for p30, gp70, and other retrovirus associated antigens detected by antibody procedures, interspecies determinants of cell mediated immunity could not be demonstrated in immune mice bearing Moloney sarcoma virus (MSV) induced tumours. Furthermore, xenogeneic immunization of mice with FL-74 cells failed to protect mice against the growth of MSV induced lymphoma or sarcoma.

Animals↗
PubMed1978

Establishment and characterization of three new continuous cell lines derived from human breast carcinomas.

Three continuous lines of mammary tumor cells (ZR-75-1, ZR-75-27, and ZR-75-30) have been established from malignant effusions of two women with breast cancer. Differentiated properties expressed by each cell line include: (a) epithelial morphology (by light and electron microscopy) resembling that of the parental tumors; (b) presence of receptors for estrogen and other steroid hormones; and (c) growth responsiveness to estrogen and/or progesterone. All three cell lines possess human karyotypes that differ from one another in modal chromosome number as well as in characteristic marker chromosomes. Two of the cultures (ZR-75-27 and ZR-75-30), although derived from the same patient, have stable differences in their karyotypes.

Breast Neoplasms↗
PubMed1976

Bvr-1, a restriction locus of a type C RNA virus in the feline cellular genome: identification, location, and phenotypic characterization in cat X mouse somatic cell hybrids.

Somatic cell hybrids were constructed between BALB/c-RAG mouse cells and feline lymphoma cells by the hypoxanthine-aminopterin-thymidine selection scheme. RAG cells spontaneously produce an endogenous B-tropic type C virus. Cat-mouse hybrids preferentially segregate feline chromosomes and retain murine chromosomes-demonstrable by karyotypic and isozyme analyses. Despite the presence of the complete mouse genome, including the viral genome, virus production was diminished to 1-5% of the levels observed in RAG parents based upon particle-associated RNA-dependent DNA polymerase (reverse transcriptase) activity in the culture fluid. Thirty-seven hybrids made on four different occasions had suppressed virus levels, and no hybrids expressed parental virus levels. Reverse selection experiments on 6-thioguanine demonstrated that a restriction gene, tentatively named Bvr-1, was linked to the feline structural genes for hypoxanthine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase; EC 2.4.4.8) and glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP+ 1-oxidoreductase; EC 1.1.1.49) in cats, probably on the X-chromosome. The genetic mode of action of Bvr-1 is trans dominant in restriction of murine leukemia virus. The restriction locus results in a block late in virus maturation but prior to release, since expression of antigens for viral structural proteins and matrue budding particles is apparent on surfaces of restriced hybrid cells but not in high-speed pellets from culture fluid of restricted cells.

Animals↗
PubMed1976

Expression of virus structural proteins on murine cell surfaces in association with the production of murine leukaemia virus.

We have used a quantitative radiolabelled antibody procedure to measure the amount of certain virus structural antigens on the surface of BALB/c RAG cells producing endogenous B-tropic type C virus. RAG cells expressed group specificities of MuLV p30 on their cell surface but did not express gp70 group specificities. However, type specificities of gp70 were expressed on BALB/c cell lines infected with Moloney leukaemia virus. The majority of p30 antigens detected on the RAG cell surface were removed by trypsin and their reappearance was prevented by cycloheximide, even in the presence of 'conditioned medium' containing MuLV. Passive adsorption of exogenous MuLV p30 to the surface of virus negative BALB/c fibroblasts reached a maximum of 20% of the protein detectable on virus producing RAG cells. These data support the hypothesis that much, but not all, of the surface p30 is expressed de novo on the cell membrane and not derived from passive adsorption of p30 released from shed virus or as a by-product of virus infection of a cell.

Adsorption↗
PubMed1974

The alpha-glycerophosphate cycle in Drosophila melanogaster. IV. Metabolic, ultrastructural, and adaptive consequences of alphaGpdh-l "null" mutations.

"Null" mutations previously isolated at the alphaGpdh-1 locus of Drosophila melanogaster, because of disruption of the energy-producing alpha-glycerophosphate cycle, severely restrict the flight ability and relative viability of affected individuals. Two "null" alleles, alphaGpdh-1(BO-1-4), and alphaGpdh-1(BO-1-5,) when made hemizygous with a deficiency of the alphaGpdh-1 locus, Df(2L)GdhA, were rendered homozygous by recombination with and selective elimination of the Df(2L)GdhA chromosome. After over 25 generations, a homozygous alphaGpdh-1(BO-1-4) stock regained the ability to fly despite the continued absence of measurable alphaGPDH activity. Inter se heterozygotes of three noncomplementing alphaGpdh-1 "null" alleles and the "adapted" alphaGpdh-1(BO-1-4) homozygotes were examined for metabolic enzymatic activities related to the energy-producing and pyridine nucleotide-regulating functions of the alpha-glycerophosphate cycle in Drosophila. The enzyme functions tested included glyceraldehyde-3-phosphate dehydrogenase, cytoplasmic and soluble malate dehydrogenase, lactate dehydrogenase, mitochondrial NADH oxidation, oxidative phosphorylation, and respiratory control with the substrates alpha-glycerophosphate, succinate, and pyruvate. These activities in any of the mutant genotypes in early adult life were indistinguishable from those in the wild type. There was, however, a premature deterioration and atrophy of the ultrastructural integrity of flight muscle sarcosomes observed by electron microscopy in the "null" mutants. These observations were correlated with a decrease in state 3 mitochondrial oxidation with alpha-glycerophosphate, succinate, and pyruvate, as well as with loss of respiratory control in adults as early as 2 wk after eclosion. Such observations, which normally are seen in aged dipterans, were accompanied by premature mortality of the mutant heterozygotes. The adapted alphaGpdh-1(BO-1-4) was identical with wild type in each of the aging characters with the single exception of lowered rates of mitochondrial oxidative phosphorylation.

Adaptation, Biological↗
PubMed1973

Segmental aneuploidy as a probe for structural genes in Drosophila: mitochondrial membrane enzymes.

A method for detecting possible structural genes in D. melanogaster based on gene dosage dependency is presented. By making thirty crosses between Y-autosome translocations, and an attached-4 cross, it is possible to produce large duplications (approximately 150 salivary gland chromosome bands in length) for every autosomal region with the exception of 83DE. The usefulness of the technique was demonstrated by dosage dependency of three known gene-enzyme systems: alpha-glycerophosphate dehydrogenase-1, alcohol dehydrogenase and malate dehydrogenase. A screen for genes affecting two enzymes localized on the inner membrane of the mitochondrion, alpha-glycerophosphate oxidase (alphaGPO) and succinic dehydrogenase (SHD), produced a dosage-sensitive region in each case. Region 50C-52E affected alphaGPO activity and region 28D-29F affected SDH activity. The latter region apparently includes the malic dehydrogenase-1 gene. The methodology and limitations of the technique are discussed.

Alcohol Oxidoreductases↗