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A Scheffer

Publications and source records attributed to A Scheffer.

4 recordsLinked to original sources
PubMed2001

DNA exhibits multi-stranded binding recognition on glass microarrays.

In the course of exploring the hybridization properties of glass DNA microarrays, multi-stranded DNA structures were observed that could not be accounted for by classical Watson-Crick base pairing. Non-denatured double-stranded DNA array elements were shown to hybridize to single-stranded (ss)DNA probes. Similarly, ssDNA array elements were shown to bind duplex DNA probes. This led to a series of experiments demonstrating the formation of multi-stranded DNA structures on the surface of microarrays. These structures were observed with a number of heterogeneous sequences, including both purine and pyrimidine bases, with shared sequence identity between the ssDNA and one of the duplex strands. Furthermore, we observed a strong binding preference near the ends of duplexes containing a 3'-homologous strand. We suggest that such binding interactions on cationic solid surfaces could serve as a model for a number of biological processes mediated through multi-stranded DNA.

DNA↗
PubMed1992

Thermal denaturation of plastocyanin: the effect of oxidation state, reductants, and anaerobicity.

The thermal stability of plastocyanin (PC) was determined as a function of oxidation state of the copper center and the presence of oxidants, reductants, oxygen, and EDTA. It was found that the copper center and its ligands play a crucial role in maintaining the stability of PC. Thermal denaturation was monitored by using far-uv circular dichroism (CD) spectra to monitor changes in secondary structure, the near-uv CD ellipticity at 280 nm to monitor changes in tertiary structure, and the absorbance at 597 nm and the 255-nm CD transition to monitor changes in the copper center. Reduced PC (Tm = 71 degrees C) was found to be more stable than the oxidized form (Tm = 61 degrees C). The Tm was increased by addition of reductants, removal of oxygen, or addition of EDTA. Two distinct denatured forms (designated D1 and D2) were separated by anion exchange fast protein liquid chromatography. Neither form contained a native copper center. Form D2 retained the characteristic 280-nm CD band but showed an altered far-uv CD spectrum. Its formation was inhibited by the addition of reductants or the removal of oxygen. It could be refolded to form native, Cu-PC upon incubation with copper plus a reductant such as dithionite. These results suggest that its formation involves the reversible oxidation of a group on the PC molecule, possibly a ligand to the copper such as Cys 84 or Met 92. Form D1 occurred in the presence of ferricyanide or at high temperatures in the presence of oxygen. EDTA inhibited its formation. Form D1 lost the 280-nm CD transition and its far-uv CD spectrum was altered. No renaturation was observed suggesting that Form D1 is the product of an irreversible oxidation step possibly involving a histidine ligand to the copper. Forms D1 and D2 are not interconvertible and represent the endpoints of two different denaturation pathways.

Anaerobiosis↗
PubMed1987

Location of genes involved in invasion and metastasis on human chromosome 7.

We have obtained evidence for the existence of genes controlling invasion and metastasis by somatic cell fusion studies. Noninvasive, nonmetastatic mouse BW5147 T-lymphoma cells were fused with invasive human T-cells. The human cells were either activated normal peripheral blood lymphocytes or leukemic T-lymphoblasts. Both fusions resulted in highly invasive human-mouse T-cell hybrids which metastasized in nude mice. Thus the genes derived from either malignant or nonmalignant but inherently invasive cells enable the T-cell hybridomas to metastasize. By continued in vitro selection for invasive cells employing monolayers of rat embryo fibroblasts followed by subcloning, we were able to isolate invasive hybrids that had lost all human chromosomes except chromosome 7. We present evidence that one or more genes residing on human chromosome 7 are necessary and sufficient for both the establishment and maintenance of invasiveness and metastatic potential of the interspecies T-cell hybrids.

Animals↗