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Biomedical subjects

I Horak

Publications and source records attributed to I Horak.

At least 73 records · Page 4Linked to original sources
PubMed1984

Evidence that a major class of mouse endogenous long terminal repeats (LTRs) resulted from recombination between exogenous retroviral LTRs and similar LTR-like elements (LTR-IS).

Two endogenous retroviral long terminal repeats (LTRs) were sequenced and compared to LTR-IS (a family of insertion-element-like sequences with structural features of solitary retroviral LTRs) and to Moloney murine leukemia virus DNA. The sequence comparisons revealed that the major difference between these two endogenous LTRs is a 190-base-pair segment which is also present in LTR-IS elements. Hybridization analysis of DNAs from several mouse species using specific probes shows linkage of the 190-base-pair segment to a LTR-IS specific fragment. It is concluded that the major class of endogenous LTRs has been generated by recombination between exogenous retroviral LTRs and LTR-IS sequences.

Animals↗
PubMed1983

Family of middle repetitive DNA sequences in the mouse genome with structural features of solitary retroviral long terminal repeats.

Screening of a 129/J mouse genomic library under nonstringent hybridization conditions with a xenotropic virus-like long terminal repeat (LTR) probe revealed a family of sequences resembling insertion elements (IS) with structural features of solitary retroviral LTRs; these are called LTR-IS. They are interspersed among variable flanking regions of mouse DNA and lack any viral structural genes. LTR-IS elements start and end with 11-base-pair inverted repeats and contain signals implicated in RNA polymerase II transcriptional regulation: C-C-A-A-T, T-A-T-A-A-A, and A-A-T-A-A-A. The members of the family are homologous, but not identical, approximately equal to 500-base-pair-long elements with 4-base-pair target-site duplications on both sites of the element. There are 500 LTR-IS per mouse haploid genome.

Bacteriophage lambda↗
PubMed1982

In vitro differentiation of F-9 teratocarcinoma cells does not induce expression of endogenous retroviral glycoprotein.

Undifferentiated F-9 teratocarcinoma cells derived from 129/J mice are induced in vitro to express several differentiation markers. Neither undifferentiated nor differentiated F-9 cells express endogenous retroviral glycoprotein (gp70), although the latter can be productively infected with exogenous retroviruses. This is discussed in context with previous findings that all antigen-activated lymphocytes of all mice express endogenous retroviral gp70.

Animals↗
PubMed1982

Expression of endogenous retroviral glycoprotein 70 by antigen-activated cytotoxic and suppressor T lymphocytes of nice.

Concanavalin A-stimulated murine spleen cells and antigen-stimulated B lymphocytes of normal mice express an antigen that reacts with goat antiserum against glycoprotein (gp) 70. Structural analysis of this antigen characterizes it as endogenous viral gp70 that is most likely of xenotropic origin. Activated nonspecific T suppressor cells and cytotoxic T lymphocytes express endogenous viral gp70, whereas nonactivated mouse T or B lymphocytes do not. The presence of endogenous retroviral gp70 is thus a novel marker for activated mouse lymphocytes in general.

Animals↗
PubMed1981

Resistance of cultures of normal T cells to infection with murine type C viruses.

Long-term continuous cultures of normal T cells were established from C57BL/6 and BALB/c mice by using conditioned medium from concanavalin A-stimulated lymphocytes. The ability of various murine type C viruses to infect these normal T cell cultures was examined and compared with their ability to infect transformed T cells. All of the viruses examined, including a thymotropic radiation leukemia virus, were unable to infect and replicate in normal T cells but readily did so in transformed T cells.

Animals↗
PubMed1981

Mechanisms in T cell leukemogenesis. II. T cell responses of preleukemic BALB/c mice to Moloney leukemia virus antigens.

The T cell responses of Moloney leukemia virus (MoLV)-infected preleukemic BALB/c mice were examined. The major in vitro response detectable was T cell blastogenesis in response to the major viral envelope protein MoLV gp71 and an internal viral protein p12. The majority of the preleukemic mice had readily detectable responses to gp71, whereas the presence of a response to p12 was less consistent. With both antigens, T cell blastogenesis showed typical antigen response characteristics similar to those detected in other immune responses to C-type viruses. Proliferation was dependent on a Thy-1+, Lyt-1+, 2- population and was macrophage-independent. In contrast to most immune responses to C-type viruses, which are temporally restricted, T cell blastogenesis was detectable throughout the preleukemic period of 4 to 16 wk of age. During this period neither gp71-specific T cells nor PHA-responsive T cells were found to express viral antigens. The correlations between T cells responding to gp71 and leukemia were examined. Under conditions in which MoLV inoculation of BALB/c mice does not induce leukemia, no T cell responses were deectable. These results suggest a causal relationship between the presence of antigen-specific T cells and the ability of MoLV to induce leukemia. The results are discussed with reference to the possible role of chronic immune stimulation in virus-induced leukemogenesis.

Animals↗
PubMed1980

Characterization of a unique defective type C virus associated with a Moloney leukemia virus-induced splenic T-cell lymphoma cell line.

Moloney leukemia virus (MoLV) induces lymphomas in BALB/c mice which either involve an immature thymic T-cell subpopulation or a splenic mature T-cell subpopulation. To investigate further the possible virological and immunological differences in these lymphomas, several lymphoma cell lines were derived. Although the majority of these cell lines expressed only the parental MoLV, one lymphoma cell line (5F4) was found which expressed only a defective virus. 5F4 virions lacked detectable reverse transcriptase activity and by immunoprecipitation lacked a serologically detectable reverse transcriptase. The lack of reverse transcriptase did not appear to be due to a deletion in the viral genome. Intracellularly 5F4 cells synthesized normal gag gene precursors but had little, if any, detectable Pr180gag-pol or an altered precursor. These results suggest that the defect of the 5F4 virus is associated with the inability to translate the appropriate precursor for reverse transcriptase. The possible origin of the detective 5F4 virus was also examined by competition radioimmunoassays. These results demonstrate that the type-specific proteins, gp71 and p12, are serologically identical to those of the endogenous ecotropic virus and distinct from the MoLV proteins. Competition assays of 5F4 cell extracts further demonstrated the lack of any detectable MoLV type-specific proteins, although the tumor was presumably induced by MoLV. The significance of these observations to leukemogenesis is discussed.

Animals↗
PubMed1978

Identification and characterization of ribosomal proteins phosphorylated in vaccinia-virus-infected HeLa cells.

Two-dimensional analysis of 32P-labelled ribosomal proteins revealed three proteins which are phosphorylated in vaccinia-virus-infected HeLa cells. All three proteins belong to the 40-S ribosomal subunits and were identified as S2, S6 and S16. The ribosomal protein S6 is phosphorylated also in uninfected HeLa cells. Phosphoserine was detected in all three proteins, phosphothreonine only in the protein S2. Phosphorylation of these ribosomal proteins in infected cells is dependent on the multiplicity of the viral infection and increases during the first six hours of infection. All three proteins are also phosphorylated in virus-infected cells treated with cycloheximide and in cells infected with ultraviolet-irradiated virus. This suggests that the phosphorylation reaction involves a vaccinia virion-associated protein kinase.

Amino Acids↗
PubMed1978

Ribosomal proteins of HeLa cells.

Ribosomal proteins from HeLa cells were analyzed by two-dimensional polyacrylamide gel electrophoresis (Kaltschmidt-Wittmann) and dodecylsulfate polyacrylamide gel electrophoresis (Laemmli). 35 proteins are associated with the small ribosomal subunit and 47 proteins with the large ribosomal subunit. The HeLa ribosomal proteins S6, S32, L40b,c, L41 and L42 are phosphorylated in vivo and in vitro. Minor differences between HeLa and rat liver ribosomal proteins were revealed by their direct coelectrophoresis.

Animals↗
PubMed1977

Acidic phosphoproteins of the 60-S ribosomal subunits from HeLa cells.

Two-dimensional analysis of the ribosomal proteins from 60-S subunits of HeLa cells revealed a triplet of acidic proteins, L40a, L40b and L40c, of identical molecular weight (13,700), which can be separated only on the basis of their charge differences. Two of the spots, L40b and L40c, become labeled after incubation of the cells with inorganic [32P]phosphate. The electrophoretic behavior and molecular weights of these proteins support the notion that the proteins L40b and L40c, are phosphorylated forms of the protein L40a. The same proteins can be phosphorylated also in vitro by a HeLa protein kinase on 60-S subunits but not on 80-S ribosomes. The inaccessibility of L40 proteins to the phosphorylation in vitro on 80-S ribosomes suggests that they are located in the interface between the 40-S and 60-S subunits.

Electrophoresis, Polyacrylamide Gel↗
PubMed1974

Interspecific recombination of mitochondrial DNA molecules in hybrid somatic cells.

The mitochondrial DNA (mtDNA) in rodent-human hybrid somatic cells was studied in strains that contain nucleotide sequences from both parental mtDNAs. A test for linkage of rodent to human mtDNA was devised on the basis of the density and sequence differences between these DNAs. When a mixture of rodent and human mtDNAs was banded in a CsCl gradient and each fraction hybridized with a mixture of complementary [(3)H]RNA transcribed from human mtDNA and complementary [(32)P]RNA transcribed from rodent mtDNA, each DNA was detected as a distinct and separate band at its expected density by specific hybridization with its complementary RNA. In some of the hybrid cell strains, the mtDNA sequences derived from the two species did not separate in the CsCl gradients. This result is interpreted as evidence for linkage between sequences from the two parental mtDNAs. While the exact nature of the linkage and the structure of the molecules containing both types of sequences are not known, the evidence supports the conclusion that the linkage is realized by a covalent bond. An event leading to the covalent bonding of these different sequences may be described as recombination. Among 18 hybrid cell strains examined, 13 contained large proportions of recombinant molecules. These molecules were found in both mouse-human and rat-human strains, and in strains containing more human or more rodent mtDNA sequences.

Animals↗
PubMed1974

The use of hybrid somatic cells as an approach to mitochondrial genetics in animals.

We have studied the fate of parental mitochondrial DNA (mtDNA) in hybrid somatic cells derived by Sendai virus-induced fusion of human cells and mouse or rat cells. Many hybrid cell strains were obtained which contained sequences from both human and rodent mtDNA after 40 to 60 population doublings. Some strains were subcloned and cultured further for up to 150 doublings; a large fraction of these strains contained both parental mtDNA sequences at that time. The relation between human and rodent mtDNA sequences was tested in some of the hybrid cell strains. In a high fraction of strains tested the human and rodent mtDNA sequences were linked to each other by what are most likely covalent bonds. This linkage may be described as "recombination" of mtDNA sequences from two different animals.

Animals↗