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Biomedical subjects

M Yaniv

Publications and source records attributed to M Yaniv.

At least 199 records · Page 11Linked to original sources
PubMed1979

Nicking-closing enzyme is associated with SV40 DNA in vivo as a sodium dodecyl sulfate-resistant complex.

A fraction of the cellular nicking-closing (NC) enzyme cosediments with SV40 chromatin isolated after Triton X-100 treatment of infected cells nuclei. Extraction of viral DNA according to the Hirt procedure by treatment of infected cells with sodium dodecyl sulfate (SDS) followed by sedimentation in sucrose gradient to separate the DNA from the bulk of detergent also revealed NC activity associated with DNA. Reconstitution experiments showed that only prebinding of the NC enzyme to DNA protects it against irreversible inactivation by SDS. These results suggest that a fraction of the cellular NC activity is indeed associated with the viral chromosome in vivo.

Chromatin↗
PubMed1979

Effects of cytosol on transcription in isolated simian-virus-40-infected nuclei.

The transcription in vitro of nuclei isolated from monkey kidney cells infected with simian virus 40 was stimulated by a cytosol fraction from the same uninfected cells. Transcription in nuclei was inhibited 60--80% by 0.1 microgram/ml of alpha-amanitin, in the presence or in the absence of the cytosol preparation. Treatment of nuclei after transcription in vitro with 0.02 M EDTA preferentially solubilized viral-specific RNA partially bound to the viral chromatin. The increase in incorporation into total RNA seen in the presence of cytosol was not paralleled by any detectable increase in transcription of viral sequences as shown by RNA . DNA hybridizations.

Amanitins↗
PubMed1979

E. coli DNA binding protein HU forms nucleosomelike structure with circular double-stranded DNA.

The incubation of the E coli DNA binding protein HU with relaxed circular SV40 DNA in the presence of pure nicking-closing enzyme introduces up to 18 negative superhelical turns in the DNA molecules as measured by agarose gel electrophoresis. The maximal density of supercoiling is obtained at a HU-DNA mass ratio of 1. Reconstituted DNA-HU complexes prefixed with glutaraldehyde appear as condensed circular structures having an average of 14 "beads" per circular SV40 DNA molecule, with a "bead" diameter of 180 +/- 23 A. The circular SV40 DNA is condensed by a ratio of 2.0-2.5 relative to naked DNA. This is similar to the ratio (2.4) measured for chromatin formed by reassociation of relaxed SV40 DNA with the four core histones.

Chromatin↗
PubMed1979

Rapid turnover of acetyl groups in the four core histones of simian virus 40 minichromosomes.

The four core histones (H2a, H2b, H3, and H4) bound to simian virus 40 minichromosomes isolated from infected cells contain rapidly labeled acetyl groups in internal positions of the histone polypeptide chain. Upon chase, these acetyl residues decay with a half-life of less than 15 min. The acetyl groups are incorporated in histones bound to mature chromosomes and not in newly synthesized histones bound to replicating viral chromosomes. The rate of acetate incorporation is not related to the degree of steady state acetylation of the individual viral or cellular histones. This rate is 4-fold higher for the viral chromatin than for its cellular counterpart isolated from the same nuclei. The possible role for histone acetylation in viral genome expression is discussed.

Acetylation↗
PubMed1979

Tropomyosin synthesis accompanies formation of actin filaments in embryonal carcinoma cells induced to differentiate by hexamethylene bisacetamide.

Hexamethylene bisacetamide (HMBA) induces in vitro the cytodifferentiation of PCC3/A/1 mouse embryonal carcinoma (EC) cells. In EC cells, actin is associated with surface structures but microfilament bundles are not seen. After 2 days of HMBA treatment, rounded EC cells are converted to flat adhesive ones with a developed cytoskeleton containing actin and tropomyosin. The ratio of actin to total proteins is constant in EC cells and their HMBA derivatives; but a striking difference is observed for one of the newly synthesized proteins (Mr 34,000) identified as tropomyosin. Synthesis of tropomyosin is followed by its association with actin microfilament bundles, as revealed by indirect immunofluorescence microscopy with specific antibodies.

Acetamides↗
PubMed1979

Nicking-closing enzyme assembles nucleosome-like structures in vitro.

The four core histones (H2A, H2B, H3, and H4) and DNA were assembled into nucleosome-like particles at physiological ionic strengths either by an extract of chromatin rich in nicking-closing activity or by the purified nicking-closing enzyme itself. When histone-DNA complexes were assembled in vitro from relaxed circular DNA, nearly physiological numbers of superhelical turns were induced in the DNA molecule. Electron microscopy of the complexes assembled by the chromatin extract revealed a beaded structure and a reduction of the contour length compared to free DNA. Micrococcal nuclease digestion of the histone-DNA complexes yielded 145-base-pair DNA fragments typical of nucleosome core particles and shorter subnucleosomal DNA fragments of discrete length.

Animals↗
PubMed1979

[Expression of ts-3 mutant of polyoma virus in mouse cells (author's transl)].

A thermosensitive mutant (ts-3) of polyoma virus produces T antigen, viral DNA and V antigen in BalbC/3T3 cells only at the permissive temperature (31 degrees C). At the non-permissive temperature (39 degrees C) these cells are unable to complement the viral defect. The pulse technique reveals only transitory cellular DNA induction between 15 and 25 h after infection at 39 degrees C. However, at both temperatures, cytoplasmic penetration is observed, and the viral DNA reaches the nuclei. Similarly, the myoblast cell line PCD2 does not complement the viral defect. In other idfferent types of cells tested (3T6, mouse kidney or secondary embryo cultures), the ts-3 mutant is expressed equally at 31 degrees C and 39 degrees C.

Animals↗
PubMed1978

Proteins bound to heterogeneous nuclear RNA of simian-virus-40-infected cells.

Heterogeneous nuclear RNA . protein (hnRNA . protein) complexes from simian-virus-40 (SV40)-infected cells late in infection contain 7--10% RNA sequences specific to SV40 DNA. The SV40 nuclear RNA . protein complexes sediment at 60--70 S. The reality and specificity of the RNA-protein association is shown in metrizamide gradients. Protein and RNA lebels of hnRNA . protein-particles in SV40-infected cells follow a parallel pattern with a peak at 1.28 g/cm2 whereas a mixture of ribosomal RNA and soluble cytoplasmic proteins is separated according to the different densities in metrizamide. Analysis of hnRNA . protein from infected cells by two-dimensional gel electrophoresis shows the presence of a number of new proteins. It is demonstrated that three of these proteins are cellular ones induced by the virus infection and hence constitute good candidates to be specific RNA . protein particles for virus nuclear RNA. The presence of actin in hnRNA . protein particles from normal and SV40-infected cells and the presence of the major capsid protein VP1 in hnRNA . protein particles from SV40-infected cells is discussed.

Base Sequence↗
PubMed1977

Preferential association of newly synthesized histones with replicating SV40 DNA.

The assembly of newly synthesized histones into nucleosomes during replication of SV40 minichromosomes in vivo was studied. Infected cells were labeled with 35S-methionine for a time shorter than that required to complete a round of viral DNA replication. Mature and replicating SV40 minichromosomes were extracted and separated by zonal sedimentation, and their histone content was analyzed by polyacrylamide gel electrophoresis (SDS and acidic urea). We show that the pulse-labeled histones associate preferentially with the replicating DNA.

Cell Line↗