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Biomedical subjects

M Tepfer

Publications and source records attributed to M Tepfer.

26 records · Page 2Linked to original sources
PubMed1992

Complete replication of a satellite RNA in vitro by a purified RNA-dependent RNA polymerase.

The 334 nucleotide R satellite RNA was used as a template for purified RNA-dependent RNA polymerase (RdRp) from cucumber mosaic virus-infected tobacco plants. The products of the reaction were dsRNA and positive-strand RNA of the same size as the R satellite RNA. Similar products were obtained when T7 RNA polymerase positive-strand transcripts of a cDNA clone of the satellite RNA, designed to have the same 5' and 3' ends as the satellite RNA, were used as templates. The formation of the positive strands demonstrates complete replication of the satellite RNA. A positive-strand transcript with 65 and 255 additional nucleotides at the 5' and 3' ends of the satellite RNA respectively was also utilized as a template by the RdRp, but only dsRNA was formed. However, no products could be detected when the RdRp was programmed with transcripts corresponding to the negative-strand satellite RNA, either with no additional terminal nucleotides or with 24 and 310 additional nucleotides at the 5' and 3' ends respectively.

Base Sequence↗
PubMed1989

Expression of a mouse metallothionein gene in transgenic plant tissues.

Three gene constructions based on a mouse metallothionein I gene (mMT-I) were introduced into tobacco using a Ri plasmid vector system to test the effectiveness of animal gene regulatory signals in plant cells. No transcription from the native mouse gene was observed. In plant cells bearing chimeric mMT-I genes in which transcription was driven by the nopaline synthase promoter, neither polyadenylation nor splicing of mMT-I pre-mRNA was observed. Detailed comparisons of mMT-I sequences with those of known plant genes were carried out; slight differences in regions of known consensus sequences may be at least partly responsible for the non-recognition of mMT-I gene regulatory signals in plant cells, though other as yet unidentified, potentially necessary sequences may also be involved.

Animals↗
PubMed1987

Expression vectors based on the Agrobacterium rhizogenes Ri plasmid transformation system.

This article describes several new expression vectors that capitalize on the ability of Agrobacterium rhizogenes to transfer DNA from its Ri plasmid to the plant nuclear genome. The intermediate vectors described include an expression cassette based on one of the three following promoters: the nopaline synthase promoter, or the cauliflower mosaic virus (CaMV) promoters responsible for transcription of either the 19S or 35S CaMV RNA. The termination and polyadenylation signals are either from the nopaline synthase gene or from CaMV. The expression micro-Ri plasmid described bears a selectable marker gene and an expression cassette cloned between the borders of the TL-region of the Ri plasmid of A. rhizogenes A4. Different strategies for using these vectors to introduce chimeric genes into plants are described, and the advantages and disadvantages of the two types of vectors are discussed.

Chromosomes, Bacterial↗
PubMed1987

Long-term acid-induced wall extension in an in-vitro system.

When frozen-thawed Avena sativa L. coleoptile and Cucumis sativa L. hypocotyl sections, under tension, are acid-treated, they undergo rapid elongation (acid-extension). The acid-extension response consists of two concurrent phases: a burst of extension which decays exponentially over 1-2 h (ExE), and a constant rate of extension (CE) which can persist for at least 6h. The extension (delta L) is closely represented by the equation: delta L = a-a e(-kt) + C t where a is the total extension of the exponential phase, k is the rate constant for ExE, and c is the rate of linear extension (CE). Low pH and high tension increased a and c, whereas temperature influenced k. The magnitude of the CE (over 50% extension/10 h), the similarity in its time course to auxin-induced growth, and the apparent yield threshold for CE indicate that CE is more likely than ExE to be the type of extension which cell walls undergo during normal auxin-induced growth.

Avena↗
PubMed1979

A Comparison of Acid-induced Cell Wall Loosening in Valonia ventricosa and in Oat Coleoptiles.

The acid-induced loosening of cell walls of Valonia ventricosa has been compared to that of frozen-thawed oat coleoptiles. The two acid extension responses are similar in regard to the shape of the pH response curve and the increase in plastic compliance induced by acid treatment. In both systems the acid response can be inhibited by Ca(2+) and in both the removal of the protons leads to a rapid termination of wall loosening. The two responses differ in several significant ways, however. The acid-induced extension of Valonia walls is more rapid than that of coleoptile walls, but of smaller total magnitude. Acid-induced loosening can occur in Valonia without the wall being under tension, but not in coleoptiles. The acid-induced extension of Valonia walls is not inhibited by 8 molar urea, whereas the response in oat coleoptiles is completely inhibited by this treatment. Ethylenediaminetetraacetate (EDTA) can cause wall loosening in Valonia comparable to that produced by low pH, whereas in coleoptiles EDTA causes a much smaller response. These results with Valonia are consistent with a mechanism of acid-induced wall loosening in which a central role is played by the displacement of Ca(2+) from the wall, while the larger part of acid-induced wall loosening in oat coleoptiles appears to be via a different mechanism.

Journal Article↗
PubMed1975

Effect of gibberellic Acid on the plasticity and elasticity of Avena stem segments.

Extensibility characteristics of Avena stem segments treated with gibberellic acid (GA) were investigated in living internodes using a microgrowth method and in partially extracted cell walls subjected to Instron extensometer analysis. Both techniques showed that treatment with GA greatly increases internodal plasticity, but has virtually no effect on internodal elasticity. The increase in plasticity occurred 1 to 2 hours after the initiation of hormone treatment, which is similar to the time of onset of GA-enhanced growth and cell wall synthesis. Cycloheximide was shown to inhibit the effect of GA on plasticity.

Journal Article↗
PubMedDate not supplied

A gene coding for a monomeric form of cucumber mosaic virus satellite RNA confers tolerance to CMV.

A gene whose transcript bears a monomeric form of cucumber mosaic virus (CMV) satellite RNA was introduced into tobacco (Nicotiana tabacum 'Xanthi' nc) plants by using an Ri plasmid-based vector system. On CMV infection, the transcript of the satellite RNA gene was used as a template to yield unit-length satellite RNA, which was efficiently amplified by the virus. Plants bearing the satellite RNA gene displayed long-term tolerance to CMV infection and were also tolerant to CMV infection by aphids, the natural vector of CMV. Implications of these results concerning the mechanism of satellite RNA replication are discussed.

Animals↗