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I Tamm

Publications and source records attributed to I Tamm.

At least 91 records · Page 5Linked to original sources
PubMed1980

Interferon effects on microfilament organization, cellular fibronectin distribution, and cell motility in human fibroblasts.

We have shown previously (Pfeffer et al., 1979, Exp. Cell Res. 121:111-120) that treatment of human fibroblasts, planted at a density of 2x10(3) cells/cm(2), with purified human fibroblasts interferon (640 U/ml) for 3 d at 37 degrees C decreases the overall rate of cell proliferation to 35-40 percent of the control value. In the present experiments we have characterized the phenotype of interferon-inhibited fibroblasts. The mean volume of trypsinized, interferon-treated cells was increased 31 percent abover that of control cells. The interferon-treated population was much more heterogeneous than the control population with respect to volume, and there was a considerable overlap in the volume distributions of the two populations. The cell surface area was, on the average, increased 65 percent after interferon treatment. More than 80 percent of the treated cells had enlarged nuclei, many of which were lobed, and the fraction of binucleated cells was increased fivefold. After interferon treatment, over 40 percent of the cells showed large actin-containing fibers in the form of multiple parallel arrays. Fewer than 5 percent of the control cells contained such large actin fibers. The number of actin fibers of all sizes was tripled in the treated fibroblasts on a per cell basis and, calculated per unit surface area of the cells, the number was increased 82 percent. In contrast, 10-nm filaments and microtubules did not appear to be increased in number per unit surface area of the cells. The increases per cell in the abundance of these structures were directly related to increased cell size. After interferon treatment, fibronection was distributed in arrays of long filaments covering most portions of the cell surface. Interferon treatment markedly decreased the rate of cell locomotion as well as membrane ruffling and saltatory movements of intracellular granules.

Cell Line↗
PubMed1979

Interferons.

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Animals↗
PubMed1979

Early termination of heterogeneous nuclear RNA transcripts in mammalian cells: accentuation by 5,6-dichloro 1-beta-D-ribofuranosylbenzimidazole.

Labeling of RNA in isolated HeLa cell nuclei in vitro reveals an abundance of short RNA chains made by RNA polymerase II. These short chains were initiated prior to isolation of the nuclei. The short abundant chains are increased in amount in nuclei isolated from cells treated with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB). Kinetic evidence indicates that the bulk of the putative heterogeneous nuclear RNA (hnRNA) precursor molecules that are terminated early in vivo are terminated approximately 100-300 nucleotides from sites of initiation. DRB increases the frequency of early termination, but there is a fraction of hnRNA precursor molecules whose elongation is not affected by DRB. Heparin is useful in studies of hnRNA transcription in isolated nuclei because it enhances chain elongation.

Amanitins↗
PubMed1979

Temporal organization of replication in DNA fibers of mammalian cells.

The extent of coordinate control over the multiple initiation events in DNA replication has been investigated in three mammalian cell lines by DNA fiber autoradiography. Quantitative estimates have been obtained of the degree of synchrony among initiations occurring on stretches of DNA. Synchrony decreases markedly with increasing distance between initiation sites in MDBK (bovine) and L929 (mouse) cells, but only slightly in muntjac cells. Possible control mechanisms for the initiation process are discussed.

Animals↗
PubMed1978

Does 3'-terminal poly(A) stabilize human fibroblast interferon mRNA in oocytes of Xenopus laevis?

Polynucleotide phosphorylase (polyribonucleotide:orthophosphate nucleotidyltransferase, EC 2.7.7.8) purified from Escherichia coli was used enzymatically to deadenylate polyadenylated human fibroblast interferon mRNA preparations obtained from human diploid fibroblasts (FS-4 strain) induced by poly(I)-poly(C) (20 microgram/ml) in the presence of cycloheximide (50 microgram/ml, 4 hr). Both the polyadenylated and the deadenylated interferon mRNA preparations were translated into biologically active human interferon when injected into oocytes of Xenopus laevis. In the oocytes the functional stability of deadenylated interferon mRNA was indistinguishable from that of polyadenylated interferon mRNA.

Animals↗
PubMed1977

A comparative study of the effects of certain halogenated benzimidazole ribosides on RNA synthesis, cell proliferation, and interferon production.

5-(or 6-)Bromo-4,5-(or 5,7-)dichloro-1-beta-D-ribofuranosylbenzimidazole, 5,6-dibromo-1-beta-D-ribofuranosylbenzimidazole, and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole show closely similar structure-activity relationships with respect to inhibition of cellular RNA synthesis, cellular proliferation, and influenza virus multiplication, and also with respect to enhancement of interferon production. The activities ofth ese compounds are ranked 20:2.5:1. The log dose-response curves constructed for inhibiton of FS-4 cell RNA synthesis show similar slopes and a leveling off at 60-70% inhibition of RNA synthesis at the highest concentrations of each compound tested. This evidence suggests that these three derivatives act through the same mechanism. It has been shown previously that the dichloro compound selectively inhibits nuclear heterogenous RNA and messenger RNA synthesis. The concentrations of the benzimidazole ribosides at which the rate of proliferation of human fibroblasts (FS-4) is reduced by 50% are as follows: monobromodichloro: 1.7 muM (0.68 mug/ml); dibromo: 12 muM (4.9 mug/ml); dichloro: 38 muM (12 mug/ml). All compounds reduce the exponential rate of cell proliferation in a dose-dependent manner. The inhibition of cell growth is reversible upon removal of the compounds from the medium. Protocols based on any one of the three halobenzimidazole ribosides give interferon yields from poly(I)-poly(C)-induced FS-4 cells which are comparable to the high yields obtained with the conventional cycloheximide-actinomycin D protocol. The enhancement of interferon yield depends on blocking of the synthesis of RNA which is involved in the shutoff of interferon production.

Benzimidazoles↗
PubMed1977

Definition of subclasses of nucleoplasmic RNA.

RNA synthesis in isolated HeLa cell nuclei prepared from cells pretreated with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) is inhibited in a time-dependent manner. After 40-min pretreatment of cells with 60 muM DRB in the presence of actinomycin D (0.04 mug/ml), the rate of RNA synthesis in isolated nuclei, measured by [(3)H]UTP incorporation, is decreased by 63%. The DRB-resistant one-third of heterogeneous nuclear is distributed over the entire size range of heterogeneous nuclear RNA with some enrichment in the 18S range, as was observed earlier by pulse-labeling whole cells. A subclass of nucleoplasmic RNA molecules is defined in the approximate size range 110 to 250 x 10(3) daltons (330-740 nucleotides). By using heparin (2 mg/ml) to block the synthesis of smaller RNA, a peak in the chain-length range 330-740 nucleotides can be clearly resolved on 2.2% polyacrylamide/1% agarose gels in nuclei from control and DRB-treated cells. The synthesis of these molecules is largely ( approximately 90%) resistant to DRB but sensitive to alpha-amanitin at 1 mug/ml. The in vitro synthesis of molecules in the 140-330 residue range is also sensitive to alpha-amanitin at 1 mug/ml, and it is not at all affected by pretreatment of cells with DRB. Although the synthesis of the RNA in both the 330-740 and the 140-330 residue size ranges appears to be catalyzed by RNA polymerase II, the results with heparin suggest that there may be reinitiation of molecules in the 140-330 size range but not in the 330-740 range in vitro. The synthesis of 4.5S RNA ( approximately 100 nucleotides) and 5S RNA (120 nucleotides) is unaffected by pretreatment of cells with DRB and, as previously reported, is catalyzed by RNA polymerase III, with reinitiation occurring in vitro. Addition of DRB directly to isolated HeLa cell nuclei in vitro has no detectable effect on the overall rate of RNA synthesis.

Amanitins↗