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Biomedical subjects

J Schell

Publications and source records attributed to J Schell.

283 records · Page 16Linked to original sources
PubMed1967

Control of malate synthase formation in Rhizopus nigricans.

The control of malate synthase formation in a fumaric acid-producing strain of Rhizopus nigricans has been found to be similar in most respects to that of isocitrate lyase, the companion enzyme of the glyoxylate bypass. A basal level is formed in a casein hydrolysate medium, which is repressed by glucose. Utilization of glucose during growth results in relief of glucose repression. Any factor which stimulates growth promotes relief of glucose repression by enhancing the incorporation of repressor metabolites derived from glucose into cell material. Thus, malate synthase formation was enhanced in glucose-containing media by the addition of zinc, or by an increase of the concentration of available nitrogen source in a synthetic medium. Both acetate and glycolate acted as apparent inducers of malate synthase, with glycolate the more effective of the two when added alone. Acetate induction was enhanced by Zn(++), however, whereas induction by glycolate was unaffected. This supports the concept that acetate stimulates formation of glyoxylate bypass enzymes by a derepression mechanism, whereas glycolate or a product derived from it acts directly as an inducer. Moreover, it is indicated that the malate synthases induced by acetate and glycolate are separate and distinct, as has been shown in Escherichia coli.

Acetates↗
PubMedDate not supplied

Light-inducible and chloroplast-associated expression of a chimaeric gene introduced into Nicotiana tabacum using a Ti plasmid vector.

A chimaeric gene, consisting of the 5'-flanking region of a member of the Pisum sativum gene family encoding ribulose 1,5-bisphosphate carboxylase linked to the coding region of a bacterial chloramphenicol acetyltransferase gene, has been introduced into the genome of the plant Nicotiana tabacum using a Ti plasmid of Agrobacterium tumefaciens. The expression of the chimaeric gene is light-inducible in chloroplast-containing transformed tissue.

Acetyltransferases↗
PubMedDate not supplied

Light regulation of plant gene expression by an upstream enhancer-like element.

Light regulates many varied physiological and developmental phenomena during plant growth and differentiation, including the formation of a photosynthetically competent chloroplast from a proplastid. The expression of ribulose 1,5-bisphosphate carboxylase small subunit (rbcS) genes is regulated by light in a development- and tissue-specific manner2,3. In some plant species, phytochrome has been demonstrated to mediate this response, and photoregulation of rbcS expression occurs at least in part at the level of transcription. We have shown previously that a 5'-noncoding fragment (4-973 base pairs (bp) upstream of the messenger RNA cap site) of the pea rbcS ss3.6 gene contains all of the nucleotide sequence information necessary to direct the photoregulated expression of a bacterial chloramphenicol acetyltransferase (cat) gene in tobacco. Consistent with these findings, Morelli et al.11 have shown by deletion analysis of a second rbcS gene promoter, that the sequences required for photoregulated expression of rbcS E9 reside within the 5'-noncoding region. They identified an upstream region of approximately 700 bp needed for maximum transcription but not light-dark regulation, and a region from -35 to -2 bp which included the TATA box and contained the necessary information for light responsiveness. We now demonstrate that regulatory sequences 5' distal to the rbcS ss3.6 TATA box and transcriptional start site not only contain the information necessary for maximum expression, but also confer photoregulation. These upstream regulatory sequences function independently of orientation when fused to their homologous promoter or a heterologous promoter.

Acetyltransferases↗
PubMedDate not supplied

Identification and role of adenylyl cyclase in auxin signalling in higher plants.

Cyclic AMP is an important signalling molecule in prokaryotes and eukaryotes, but its significance in higher plants has been generally doubted because they have low adenylyl cyclase activity and barely detectable amounts of cAMP. Here we used activation T-DNA tagging to create tobacco cell lines that can proliferate in the absence of the phytohormone auxin in the culture media. The sequence tagged in one line, axi 141, was used to isolate a complementary DNA encoding adenylyl cyclase, the first from a higher plant. Sequence analysis reveals that the tobacco adenylyl cyclase is probably soluble, contains characteristic leucine-rich repeats, and bears similarity with adenylyl cyclase from the yeast Schizosaccharomyces pombe. Expression of the cDNA in Escherichia coli results in an increase in endogenous cAMP levels, and in yeast its expression functionally complements the cry1 mutation. Tobacco protoplasts treated with cAMP, or the adenylyl cyclase activator forskolin, no longer require auxin to divide. This finding, together with the observation that the adenylyl cyclase inhibitor dideoxyadenosine inhibits cell proliferation in the presence of auxin, suggests that cAMP is involved in auxin-triggered cell division in higher plants.

Adenylyl Cyclases↗
PubMedDate not supplied

Transfer, maintenance, and expression of bacterial Ti-plasmid DNA in plant cells transformed with A. tumefaciens.

The mechanism of induction of the plant cancer crown gall by Agrobacterium tumefaciens has been briefly described. The salient points are as follows. 1. Large plasmids of molecular weight (100 to 150) S 10(6), called Ti-plasmids, are essential to the transformation process. 2. Ti-plasmids carry a DNA segment that can be transferred to, and maintained and expressed in, transformed plant cells. 3. This DNA segment has been identified both by direct hybridization experiments between Ti DNA fragments and crown gall DNA and by the study of a deletion mutant of a Ti-plasmid. 4. Indirect evidence suggests that genes involved in the synthesis of abnormal amino acids (such as octopine and nopaline) by crown gall cells, and known to be carried on the Ti-plasmids, are in fact located on the DNA segment that is transferred to the plant cells. 5. Ti-plasmids are efficient conjugative plasmids, since they can promote their own transfer by conjugation to various plasmid-free bacterial strains. Their conjugative properties may be involved also in the Ti DNA transfer from Agrobacterium to plant cells. 6. Preliminary evidence indicates that the transferable segment of the Ti-plasmid has the structure of a transposon, since it appears to be flanked by a sequence exhibiting most of the properties of the sequences that border the known bacterial drug-resistance gene transposons.

Cell Transformation, Neoplastic↗