Biomedical subjects

A J Matzke

Publications and source records attributed to A J Matzke.

47 records · Page 3Linked to original sources

PubMed1991

Differential inactivation and methylation of a transgene in plants by two suppressor loci containing homologous sequences.

In a previous study on doubly transformed tobacco plants, we observed the unexpected inactivation in trans of T-DNA-I (encoding KanrNOS) following the introduction into the same genome of an unlinked copy of T-DNA-II (encoding HygrOCS). This inactivation, which probably resulted from interactions between homologous regions on each T-DNA, was correlated with methylation in the nospro, which controlled the expression of both the nptII and nos genes. In this paper, we show that the inactivation and methylation of the nos(pro)nptII gene in the presence of a suppressor T-DNA-II locus can be either complete (epistasis) or partial (cellular mosaicism). In plants showing partial suppression, the strength of the Kanr phenotype, which apparently reflected the proportion of cells expressing the nptII gene, was inversely correlated with the degree of methylation of the nos(pro). The extent of nos(pro) methylation decreased progressively in successive generations as suppressor T-DNA-II loci were crossed out. The strength of the Kanr phenotype was improved and nos(pro) methylation was less extensive in first generation Kanr progeny obtained from outcrossing with untransformed tobacco than from self-fertilization.

Amino Acid Oxidoreductases↗

PubMed1990

Detection of a large cation-selective channel in nuclear envelopes of avian erythrocytes.

To determine whether the nuclear envelope of eukaryotic cells has the capability to regulate ion fluxes, we have used the patch-clamp technique to detect ion channels in this membrane system. Since possible sites for ion channels in the nuclear envelope include not only the nuclear pores, but also both the inner and outer nuclear membranes, we have patched giant liposomes composed of phosphatidylcholine and nuclear envelope fragments isolated from mature avian erythrocytes. A large, cation-selective channel with a maximum conductance of approximately 800 pS in symmetrical 100 mM KCl was detected. This channel is a possible candidate for a nuclear pore.

Animals↗

PubMed1990

Deletion analysis of a zein gene promoter in transgenic tobacco plants.

A zein gene (Z4) promoter containing 886 bp upstream from the transcription start site has been shown previously to be active specifically in the endosperm of transgenic tobacco seeds. To investigate the region required for this tissue-specific activity, deletions of the Z4 promoter were constructed and placed upstream of the beta-glucuronidase (GUS) reporter gene. When these deletions were tested in transgenic tobacco plants, seed-specific GUS activity, which reached a peak between 15 and 19 DAP, was observed for promoters extending from -886 to -174. Interestingly, the 174 bp promoter lacked the complete 15 bp consensus sequence found in the same position in all zein genes so far sequenced. With the next shorter promoter in the deletion series (79 bp), which just included the CAAT and TATA elements, negligible GUS activity was observed in seeds. The results demonstrated that 174 bp upstream of the transcription start site are sufficient for tissue-specific and temporally regulated activity of the Z4 promoter in tobacco. At most, two-fold enhanced activity was observed with additional 5' sequences up to -886.

Base Sequence↗

PubMed1990

A 41-42 bp tandemly repeated sequence isolated from nuclear envelopes of chicken erythrocytes is located predominantly on microchromosomes.

To study whether specific DNA sequences are associated with nuclear membranes, residual DNA was extracted from DNase-treated nuclear envelopes prepared from erythrocytes of adult chickens (Gallus domesticus). This DNA was then blunt-end ligated into a bacterial plasmid vector. DNA blot analysis and nucleotide sequence determination revealed that approximately 30% of the cloned fragments consisted of different multiples of a 41-42 bp tandemly repeated, partially symmetrical sequence. In situ hybridization to chicken chromosomes demonstrated that the sequence was located primarily on microchromosomes, although some hybridization was also observed to macrochromosomes 7 and 8. Digestion of chicken DNA with any of a number of restriction enzymes did not completely reduce the intensity of a high molecular weight band to which the repeated sequence hybridized. These results, along with those obtained from in situ hybridization, suggested that many copies of this sequence are organized into large tandem arrays, and are not dispersed in many shorter repetitive blocks throughout the chicken genome. Although the repetitive sequence constituted approximately 10% of the chicken genome, it did not hybridize to quail or turkey DNA.

Animals↗

PubMed1989

Reversible methylation and inactivation of marker genes in sequentially transformed tobacco plants.

Doubly transformed tobacco plants were obtained following sequential transformation steps using two T-DNAs encoding different selection and screening markers: T-DNA-I encoded kanamycin resistance and nopaline synthase; T-DNA-II encoded hygromycin resistance and octopine synthase. A genetic analysis of the inheritance of the selection and screening marker genes in progeny of the doubly tranformed plants revealed that the expression of T-DNA-I genes was often suppressed. This suppression could be correlated with methylation in the promoters of these genes. Surprisingly, both the methylation and inactivation of T-DNA-I genes occurred only in plants containing both T-DNAs: when self-fertilization or backcrossing produced progeny containing only T-DNA-I, expression of the genes on this T-DNA was restored and the corresponding promoters were partially or completely demethylated. These results indicated that the presence of one T-DNA could affect the state of methylation and expression of genes on a second, unlinked T-DNA in the same genome.

Journal Article↗

PubMed1988

Endosperm-specific activity of a zein gene promoter in transgenic tobacco plants.

Transgenic tobacco plants containing maize gene (Z4) encoding a 23-kd zein protein, which is normally synthesized in the endosperm of maize seeds, were obtained using a modified Ti plasmid vector. Although a polyadenylated transcript homologous to the Z4 gene was present in the seeds of some of these transgenic plants, zein protein could not be detected in any of the plants tested (35 total). To simplify the analysis of the tissue specificity of the Z4 promoter (Z4(pro)) in different organs of transformed tobacco plants, additional transgenic plants containing the chimeric genes Z4(pro)-CAT and Z4(pro)-GUS were produced. Very weak seed-specific CAT activity was observed in one out of ten Z4(pro)-CAT-transformed plants. When the more sensitive GUS assay system was used to evaluate Z4(pro) activity in tobacco, it could be shown in all 11 transgenic plants obtained that GUS activity was restricted to the endosperm tissue of transgenic tobacco seeds. To study the synthesis and stability of the zein proteins in different organs of transgenic tobacco plants, the Z4 protein-coding region and also a cDNA clone (A30) encoding a 19-kd zein protein were placed under the control of the 35S promoter (35S(pro)) of cauliflower mosaic virus. Undegraded zein proteins of both size classes were detected in roots, leaves and endosperm tissue, but not embryos, of mature seeds from 35S(pro)-zein-transformed plants. The zein proteins did not appear to be broken down during tobacco seed germination; synthesis of zeins began in green cotyledons.

Journal Article↗

PubMed1984

Transcription of a zein gene introduced into sunflower using a Ti plasmid vector.

A maize genomic clone containing a zein gene (Z4) was inserted into the T-region of the T37 Ti plasmid. Agrobacterium tumefaciens cells carrying this modified Ti plasmid were used to inoculate sunflower stemlets. Callus tissue active in nopaline synthesis was grown from a single transformed cell. DNA analysis of this tissue showed that the zein gene plus T-DNA was present in approximately 12 copies per diploid sunflower genome. A 1000 +/- 100 base RNA homologous to a zein probe could be isolated from the engineered sunflower tissue and the 5' end of this RNA was determined by S1 nuclease mapping. Two transcription start sites were detected. The positions of these transcription start sites and the ratio of the amounts of the two transcripts are identical for the Z4 gene in sunflower and in maize endosperm. Although the zein RNA isolated from the engineered sunflower tissue could be translated in a wheat germ system to yield an immuno-precipitable protein of the expected mol. wt., the presence of the zein protein in the sunflower tissue could not be demonstrated.

DNA, Recombinant↗

PubMed1983

Regeneration of intact tobacco plants containing full length copies of genetically engineered T-DNA, and transmission of T-DNA to R1 progeny.

Cloned DNA sequences encoding yeast alcohol dehydrogenase and a bacterial neomycin phosphotransferase have been inserted into the T-DNA of Agrobacterium tumefaciens plasmid pTiT37 at the "rooty" locus. Transformation of tobacco stem segments with the engineered bacterial strains produced attenuated crown gall tumors that were capable of regeneration into intact, normal tobacco plants. The yeast gene and entire transferred DNA (T-DNA) were present in the regenerated plants in multiple copies, and nopaline was found in all tissues. The plants were fertile, and seedlings resulting from self-pollination also contained intact and multiple copies of the engineered T-DNA. Expression of nopaline in the germinated seedlings derived from one regenerated plant was variable and did not correlate with the levels of T-DNA present in the seedlings. Preliminary evidence indicates that nopaline in progeny of other similarly engineered plants is more uniform. The disarming of pTiT37 by insertions at the "rooty" locus thus appears to produce a useful gene vector for higher plants.

Alcohol Oxidoreductases↗

PubMed1981

Site-specific insertion of genes into T-DNA of the Agrobacterium tumor-inducing plasmid: an approach to genetic engineering of higher plant cells.

This paper presents a method for insertion of genetic material into a specific site in T-DNA, the portion of Agrobacterium tumor-inducing (Ti) plasmid that becomes incorporated into the nuclear DNA of transformed plant cells when crown gall tumors are incited by this plant pathogen. The three stages of our procedure are as follows: 1. A T-DNA subfragment cloned in pBR322 is cleaved by a restriction endonuclease at a unique central site and target DNA (a kanamycin resistance marker) is ligated into this site. 2. The resulting recombinant plasmid is purified and cleaved with EcoRI; the resulting fragment bearing the kanamycin resistance marker is ligated into the unique EcoRI site of pRK290, a wide-host-range plasmid. 3. The pRK290 recombinant plasmid is transformed into an agrobacterium tumefaciens strain containing a wild type Ti plasmid. Double recombination between the altered T-DNA fragment of the clone and its wild-type counterpart in the Ti plasmid is selected for by introduction of R751-pMG2, a plasmid incompatible with pRK290. The approach described here can be adapted for introducing genes into higher plant cells with the Ti plasmid as vector. It can likewise be used for site- or fragment-specific mutagenesis of the Ti plasmid as a means of detailed functional analysis.

DNA↗

PubMed1980

Mechanism of translocation: relative arrangement of tRNA and mRNA on the ribosome.

AcPhe-tRNAPhe from yeast can be photocross-linked to poly(U) on Escherichia coli ribosomes. The photoreaction occurs at the wybutine base situated next to the 3' side of the anticodon. The kinetics and efficiency of crosslinking of AcPhe-Phe-tRNA are the same at both the acceptor site and the peptidyl site. Therefore, the orientation of wybutine with respect to the mRNA is similar in both the pretranslocational and posttranslocational states. AcPhe-Phe-tRNA crosslinked at the acceptor site can still be translocated to the peptidyl site, demonstrating that tRNA and mRNA are transported together. The experiments support a model of translocation in which the conformation of the anticodon loop of tRNA is similar in both the peptidyl site and the acceptor site.

Anticodon↗

PubMed1980

Photo-induced crosslinking between phenylalanine transfer RNA and messenger RNA on the Escherichia coli ribosome.

Crosslinking between phenylalanyl transfer RNA from brewer's yeast and poly(U) can be obtained when ribosomal complexes are irradiated at > 300 nm; the ribosomal complexes were formed by enzymatic binding of the tRNA. The crosslinked product was isolated on oligo(dA)-cellulose columns. The experiments suggest that the photo-crosslinking occurs via the wybutine in the anticodon loop of the tRNA. This system can be used to study interactions between tRNA and messenger RNA on the ribosome.

Escherichia coli↗