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Biomedical subjects

H L Ozer

Publications and source records attributed to H L Ozer.

At least 55 records · Page 3Linked to original sources
PubMed1980

Temperature-sensitive mutants of BALB/3T3 cells. III. Hybrids between ts2 and other mouse mutant cells affected in DNA synthesis and correction of ts2 defect by human X chromosome.

Complementation studies were performed with ts2, a mouse 3T3 cell mutant temperature sensitive (ts) for cell and viral DNA synthesis. The ts phenotype is corrected by non-ts mouse or human cells and a non-DNA ts mutant. This gene had been localized to a region on the human X chromosome near the HPRT locus based on isozyme and karyotype analysis of hybrids. Unusually rapid loss and fragmentation of human chromosomes occurs in hybrids with ts2. Hybrids between ts2 and other DNA- ts mutants of mouse cells did not show complementation of the growth phenotype.

Animals↗
PubMed1979

Ordered replication of DNA sequences: synthesis of mouse satellite and adjacent main band sequences.

The replication of mouse satellite DNA was delayed when synchronized 3T3 cells were exposed to low concentrations of hydroxyurea during S phase, It appears that the onset of satellite replication is not a time dependent event, but instead requires that a certain amount of main band DNA be synthesized first. Using hydroxyapatite chromatography and S1 nuclease digestion, a procedure was developed to quantitate the synthesis of both satellite and neighboring main band sequences. The replication kinetics of satellite determined by this method agree with previous estimates. Main band sequences adjacent to satellite appear to replicate in concert with satellite DNA. The results are discussed and related to the limitations of the techniques utilized.

Animals↗
PubMed1978

Expression of transformation in cell hybrids. II. Nonsuppression of the transformed phenotype in hybrids between a chemically transformed and nontransformed derivatives of Balb/3T3.

Hybrid clones derived from a nitrosocarbaryl-transformed Balb/3T3 cell line, Clone H, and a nontransformed cell line THO2 resemble the transformed parent in the clone morphology, higher saturation density, colony formation in medium with reduced serum concentration, growth in agarose and ability to form clones on Balb/3T3 monolayer. Results are discussed in the framework of genetic models which permit or require dominant mutations for the expression of transformed phenotype.

Animals↗
PubMed1978

A murine cell possessing a dominant mutation affecting the regulation of interferon production: characterization by intraspecific hybrids.

Using intraspecific hybrids, we have demonstrated the dominant nature of two phenotypic markers present in a mutant mouse 3T6 cell line, designated 3T6-VrB2. These are, resistance to virus infection (Vr) and semiconstitutive synthesis of interferon (IFsc). Hybrids were formed by polyethylene glycol-mediated fusion between 3T6-VrB2, or its parent 3T6, and 2TG0-13, a triply marked derivative of mouse 3T3 cells. When tested for the Vr marker, 3T6-VrB2 X 2TG0-13 hybrid clones displayed a level of resistance to virus infection which was equal to or greater than that of 3T6-VrB2. Similarly, when tested for the IFsc marker, these hybrid clones were found to possess the capacity to confer an interferon-induced antiviral state in mouse L929 cells upon cocultivation. By comparison, clones derived from 3T6 X 2TG0-13 fusions produced high levels of virus and failed to confer an interferon-induced antiviral state in L929 cells.

Animals↗
PubMed1977

Replication kinetics of three DNA sequence families in synchronized mouse cells.

Balb/C3T3 cells entered the quiescent Go state following serum deprivation. On addition of fresh serum, more than 95% of the culture resumed growth, but with asynchronous kinetics. If hydroxyurea were added just before the first cells reached S phase, at at least 90% of the cells accumulated at the Gl/S border over the next ten hours. When the block was removed, the culture moved synchronously into S phase. As the cells traversed S, the replication kinetics of three classes of rapidly renaturing DNA were analyzed. Main band highly repeated DNA and foldback DNA replicated continuously, In contrast, satellite DNA replication did not commence until three hours into S, whereupon its rate of synthesis increased ver rapidly, reaching a maximum with the next two hours. These results are discussed in the light of earlier work utilizing other methods of cell synchronization.

Animals↗
PubMed1977

Common structural antigen of papovaviruses of the simian virus 40-polyoma subgroup.

An antigenic determinant common to the major capsid polypeptide (VP1) of simian virus 40 (SV40) and polyoma virus is described. Antisera prepared against intact viral particles reacted only with cells infected with the homologous virus by immunofluorescence tests (IF). However, antisera prepared against disrupted SV40 particles reacted in IF with both polyoma- and SV40-infected permissive cells. The cross-reaction with polyoma was localized to VP1 by the following evidence. (i) The IF cross-reaction was inhibited by preincubation of the antiserum with purified SV40 VP1; (ii) purified radiolabeled polyoma VP1 was precipitated by the cross-reactive serum, and this reaction was inhibited by unlabeled SV40 VP1; (iii) other antisera prepared against purified SV40 VP1 or polyoma VP1 reacted in IF with both SV40- and polyma-infected permissive cells. These cross-reacting antisera also reacted in IF with permissive cells infected with BK virus, rabbit kidney vacuolating virus, and the stumptailed macaque virus, suggesting that all members of the polyoma-SV40 subgroup share a common antigenic determinant located in their major capsid polypeptides.

Antigens, Viral↗
PubMed1977

Identification of simian virus 40 protein A.

A large simian virus 40 (SV40)-specific protein can be efficiently immunoprecipitated from infected cell extracts with antisera obtained from hamsters bearing SV40-induced tumors. The protein has an apparent molecular weight of 88,000 to 100,000 with respect to markers with known molecular weights, but behaves anomalously on sodium dodecyl sulfate (SDS)-polyacrylamide gels. Cell lines infected by two different strains of SV40 synthesize immunoreactive proteins that differ slightly in mobility during SDS-polyacrylamide gel electrophoresis, evidence that the protein is coded for by the virus. These differences in protein size correlate with differences in the electrophoretic mobility of viral DNA fragments obtained by digestion with HindII and III restriction enzymes. The size of the viral capsid proteins VP2 and VP3 also varies with the strain of virus. dl-1001, a constructed deletion mutant that lacks part of the SV40A gene, directs the synthesis of a 33,000-dalton polypeptide that is not detected in cells infected with wild-type virus. The deletion fragment, like the larger protein, is phosphorylated. Maps of tryptic peptides from the 88,000- to 100,000-dalton protein and the 33,000-dalton fragment show common peptides and provide strong direct evidence that the proteins are products of the SV40 A gene. The deletion fragment reacts with antitumor sera and binds to double-stranded DNA in the presence of the complete A protein.

Capsid↗
PubMed1976

Expression of transformation in cell hybrids. I. Isolation and application of density-inhibited Balb/3T3 cells deficient in hypoxanthine phosphoribosyltransferase and resistant to ouabain.

A cell line, THO2, was isolated from Balb/3T3 clone A31 after sequential nitrosoguanidine treatments and selection for resistance to 6-thioguanine and ouabain. THO2 retains the properties of density-dependent inhibition of growth and serum dependence of DNA synthesis characteristic of 3T3. The codominant expression of ouabain resistance and inability of THO2 to utilize exogenous hypoxanthine in the presence of aminopterin allows isolation of somatic cell hybrids involving THO2 and any ouabain-sensitive, hypoxanthine phosphoribosyltransferase-positive cell line. Hybrid clones derived from THO2 and SV40-transformed cells show dominant expression of the transformed phenotype with respect to multilayered arrangement of cells and ability to synthesize DNA in 1% calf-serum medium.

Cell Line↗
PubMed1976

Temperature-sensitive mutants of Balb/3T3 cells: description of a mutant affected in cellular and polyoma virus DNA synthesis.

A temperature-sensitive Dna- mutant (ts-2) of the mouse cell Balb/3T3 is characterized. Studies with synchronized cells indicate that the defect is in DNA synthesis itself, rather than in progress toward its initiation. ts-2 supports polyoma DNA synthesis after infection at 33degreesC but not at 38degreesC. Viral DNA synthesis begun at 33degreesC is inhibited upon shift to 38degreesC. A procedure is proposed by which viral DNA synthesis can be used to distinguish different classes of cell Dna- mutants.

Cell Division↗
PubMed1976

Endonucleases and simian virus 40 virions: origin of a virion-associated endonuclease.

The origin and role of the endonuclease activity associated with purified virions of simian virus 40, previously described by this and other laboratories, have been further investigated. We found that the enzymatic activity from virions of temperature-sensitive (ts) mutants is not more heat labile than that from wild-type virions. This result was obtained for a variety of ts mutants, including three of the tsA class, and in experiments in which the enzyme was tested in both the presence and absence of viral particles. Comparison of the viron enzyme with endonucleases prepared from either serum or nuclei of uninfected cells reveals a similarity between the viron and serum enzymes based on chromatographic behavior and relative activity with different cations. Virus particles prepared free of this endonuclease were still infectious. We were unsuccessful in uncovering endonuclease in such preparations upon disruption. These data emphasize the necessity for caution in interpreting the role of particle-associated enzymes.

Animals↗
PubMed1975

Comparison of intracytoplasmic A particles and intracisternal A particles.

Intracytoplasmic A particles and intracisternal A particles are associated with mouse tumors of various types, and both can coexist in the cytoplasm of the same cell. The designation of both as A particles is based on the recognition that they share morphological similarities. A comparison of purified isolates of these two particles reveals that the structural protein profiles are different, but that there is some antigenic cross-reaction as demonstrated by immunodiffusion and complement fixation. This result does not appear to involve the major structural protein of intracisternal A particles, but may reflect the presence of common antigenic determinants located on minor proteins.

Animals↗
PubMed1974

Translation of mRNA from simian virus 40-infected cells into simian virus 40 capsid protein by cell-free extracts.

Messenger RNA was isolated from simian virus 40 (SV40)-infected and mock-infected cells by chromatography on poly(U) sepharose. When added to cell-free extracts from Chinese hamster ovary cells or rabbit reticulocytes, RNA from the infected cells, but not from mock-infected cells, stimulated synthesis of the major SV40 capsid protein. Identification of this species was done by sodium dodecyl sulfate gel electrophoresis, peptide mapping, and immunoprecipitation. The in vitro synthesized capsid protein was slightly different from virion assembled capsid protein, as shown by separation upon chromatography on hydroxylapatite and by minor differences in the peptide map.

Animals↗
PubMed1974

Antigenic phenotypes and complementation groups of temperature-sensitive mutants of simian virus 40.

The antigenic phenotypes of several temperature-sensitive mutants of simian virus 40 were determined by an immunofluorescence microtechnique that allowed a very high degree of internal control for the conditions of virus infection and antigenic staining. The tumor (T), U, capsid protein (C), and virion (V) antigens were investigated. Productive infection in monkey cells and abortive infection in mouse cells were simultaneously monitored for antigen production at both permissive and restrictive temperatures. Complementation analyses of the mutants demonstrated two complementing groups (A and B) and one noncomplementing group ((*)). One of the complementing groups could be subdivided into two subgroups having very different antigenic phenotypes. The following phenotypes were observed at the restrictive temperature in monkey cells. (i) The noncomplementing group produced none of the antigens. (ii) Group A induced T antigen in moderately but consistently reduced numbers of cells. Other antigens were markedly reduced or absent. (iii) Some of the group B mutants produced T antigen but little or no U and V antigens. The C antigen appeared in the nucleolus and cytoplasm of this subgroup. (iv) In the other group B mutants, antigen synthesis was not altered. Similar phenotypes were observed in mouse cells, except that U, C, and V antigens could not be detected during either the mutant or wild-type virus infections at any temperature.

Animals↗
PubMed1974

Altered protein metabolism in infection by the late tsB11 mutant of simian virus 40.

The DNA of the temperature-sensitive mutant tsB11 is replicated at the same rate as the DNA of wild-type virus in infection at the restrictive temperature. The progeny mutant DNA cannot be distinguished from wild-type DNA by gel electrophoresis and is assembled into a nucleoprotein complex with the same velocity sedimentation characteristics as the wild-type complex. Analysis of in vivo protein synthesis by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoprecipitation techniques demonstrated that the capsid components VP1, VP2, and VP3 of the mutant and wild-type virus are synthesized at a similar rate, but VP1 fails to accumulate within cells infected by tsB11. Furthermore, VP1 is located predominantly in the cytoplasmic rather than in the nuclear fraction of extracts from cells infected by the mutant. Immunofluorescent studies localized virion antigen within the nucleolus as well as the cytoplasm. The altered intracellular distribution and stability of VP1 suggest that it may be the mutant protein of tsB11. The synthesis of a 72,000 dalton protein is consistently induced in significant quantity in cells infected by tsB11 at the restrictive temperature. A protein of the same apparent molecular weight is present in smaller quantities in uninfected cells and is only slightly increased in quantity in cells infected by wild-type virus.

Animals↗